<p>Luffy's Haki ability is called Busoshoku: Koka. Koka means hardening. Luffy's body is made of rubber. Oda is quite clearly referring to hardened rubber, or vulcanized rubber, which is black. (Compare images below)</p>

<p><img src="https://i.sstatic.net/C6LIL.png" alt="Luffy&#39;s hardened arm">
<img src="https://i.sstatic.net/dATiX.jpg" alt="Vulcanized rubber"></p>

CC BY-SA 3.0
2014-08-07T04:20:05.373Z
+1 Nice find. But then why would non-rubber, like Smoker and Vergo, people turn black when they use Haki?
TAAPSogeking
CC BY-SA 3.0
2014-08-14T09:12:17.387Z
I always assumed the black coloring was just to give the audience something to identify a "haki punch". Since the whole haki thing is only properly explained during the 2y gap, it makes sense to start differentiating visually between normal and haki attacks from that point on (with maybe some subtle hinting beforehand?).
Kevin
CC BY-SA 3.0
2015-05-03T12:31:30.147Z
@TAAPSogeking Luffy is the main character, and he is rubber, so Oda must have focussed his thoughts more on what Luffy's Haki would look like. Then he decided that for other people's Haki, he would use the same "color coding" to keep things simple, and avoid questions like, "why does Mingo's Haki look pink?" :)
Masked Man
CC BY-SA 3.0
2016-10-27T16:07:32.170Z
@Kevin Hnestly, looking back, I think the most logical reason it was never colored in, as an IN universe kind of deal, is because none of the straw hats could detect it before. The haki Arrows that pierced stone were easily shattered in luffys hands, and he had no idea why. After the 2y time skip, they all learned how to use it, so naturally they could begin detecting it. I know more than one example of strange powers that were revealed to be invisible things. Such as YuYu Hakusho's bomber guy, and the Invisible hands from Re:Zero
Ryan
CC BY-SA 3.0
2013-11-04T08:35:03.820Z
2013-11-04T08:35:03.820Z
Masked Man
<p>It depends on how dense the haki (invisible armor) they use. When garp use haki to hurt luffy, he applied just a small amount so that it doesn't really hurt or can cause serious injury. That explains alot right? When you applied a vast amount of haki on your body .. it will turn black.. because of the density of the haki you applied on it. if it is a small amount.. then it's like invisible..</p>

CC BY-SA 3.0
2014-01-12T06:54:30.183Z
2014-01-12T06:54:30.183Z
one piece fanatic
<p>In the pre-timeskip, use of Busoshoku Haki as "invisible armor" was shown as a swift percussion forming a light-blue beam, similar to lightning, while in the manga, it is shown simply as an amplified impact, nothing else visible is shown... from wiki :v</p>

CC BY-SA 3.0
2014-08-14T06:08:30.490Z
2014-08-14T06:08:30.490Z
Rafu
<p>The physical strength attribute of haki works as an "invisible armor" called <a href="http://onepiece.wikia.com/wiki/Haki/Busoshoku_Haki">Busoshoku Haki</a>.
The raise in density &amp; thus, black coloring of a body part is in this haki category called <strong>Busoshoku: Koka</strong>. The sky priests aren't listed as users of either forms of this haki, but they did demonstrate haki abilities such as <a href="http://onepiece.wikia.com/wiki/Haki/Kenbunshoku_Haki">Kenbunshoku Haki</a> which they called Mantra.</p>

<p>So yes, it is a special type of haki. </p>

<p>But reasons for not using it pre-timeskip span from it not being a fleshed out idea yet to something saved for the new world or it's just a serious assault that people inexperienced can't reach without proper training (since Enel never had too many challenges to increase his potential) to people who could do it were just holding back (because Garp wanted to raise Luffy... not kill him). </p>

CC BY-SA 4.0
2022-08-10T08:04:16.667Z
Yeah, so basically they are both the same, but Koka is thicker and harder and drains haki faster. It is not specific to Luffy or based on hardened/vulcanized rubber (as another answer here suggests), since many people in the new world also can use Koka. It is also why the axe of Boo from the happou navy was mentioned to be haki imbued but wasn't black (chapter 715, p. 14). He wasn't using Koka. Both are armament haki, just different strengths/levels of it.
Skillzore
CC BY-SA 3.0
2013-10-07T20:12:10.850Z
2013-10-07T20:12:10.850Z
Daz C
<p>Before the time skip, characters like Garp and the Priest of Sky Island, used Haki to deal damage to Luffy via a blunt attack, which would have been impossible otherwise. Also, Haki was used by both sides during the Summit War. None of these people turned black. </p>

<p>But after the time skip, when Luffy used Haki against Hordy, he partially turned black. And during his fight with Z, they both turned partially black. Is this a special type of Haki? Is there any reason why they change colors and if so why black?</p>

CC BY-SA 3.0
2013-11-06T02:37:30.323Z
I thought it was the impact dial that the priest of Sky island used to hurt Luffy, not some form of haki.
nix
CC BY-SA 3.0
2013-11-08T00:41:18.917Z
@NixR.Eyes You are right, but the priest and Enel still usesd Kenbunshoku Haki, which they called Mantra,to sense movements.
TAAPSogeking
<one-piece>
Why does the use of Haki turn part of your body black?
# Why does the use of Haki turn part of your body black?
Posted by: username_0 on 2013-10-07
Before the time skip, characters like Garp and the Priest of Sky Island, used Haki to deal damage to Luffy via a blunt attack, which would have been impossible otherwise. Also, Haki was used by both sides during the Summit War. None of these people turned black.

But after the time skip, when Luffy used Haki against Hordy, he partially turned black. And during his fight with Z, they both turned partially black. Is this a special type of Haki? Is there any reason why they change colors and if so why black?
**Tags:** one-piece
> **Comments:**
> **username_1**: I thought it was the impact dial that the priest of Sky island used to hurt Luffy, not some form of haki.  
> **username_0**: @NixR.Eyes You are right, but the priest and Enel still usesd Kenbunshoku Haki, which they called Mantra,to sense movements.  
---
## 4 answers
### Answer by username_7 on 2013-10-07. Score: 10 | Accepted answer
The physical strength attribute of haki works as an "invisible armor" called [Busoshoku Haki](http://onepiece.wikia.com/wiki/Haki/Busoshoku_Haki).
The raise in density & thus, black coloring of a body part is in this haki category called **Busoshoku: Koka**. The sky priests aren't listed as users of either forms of this haki, but they did demonstrate haki abilities such as [Kenbunshoku Haki](http://onepiece.wikia.com/wiki/Haki/Kenbunshoku_Haki) which they called Mantra.

So yes, it is a special type of haki.

But reasons for not using it pre-timeskip span from it not being a fleshed out idea yet to something saved for the new world or it's just a serious assault that people inexperienced can't reach without proper training (since Enel never had too many challenges to increase his potential) to people who could do it were just holding back (because Garp wanted to raise Luffy... not kill him).
> **Comments:**
> **username_8** (2022-08-10): Yeah, so basically they are both the same, but Koka is thicker and harder and drains haki faster. It is not specific to Luffy or based on hardened/vulcanized rubber (as another answer here suggests), since many people in the new world also can use Koka. It is also why the axe of Boo from the happou navy was mentioned to be haki imbued but wasn't black (chapter 715, p. 14). He wasn't using Koka. Both are armament haki, just different strengths/levels of it.  
---
### Answer by username_2 on 2013-11-04. Score: 11
Luffy's Haki ability is called Busoshoku: Koka. Koka means hardening. Luffy's body is made of rubber. Oda is quite clearly referring to hardened rubber, or vulcanized rubber, which is black. (Compare images below)

![Luffy's hardened arm](https://i.sstatic.net/C6LIL.png)
![Vulcanized rubber](https://i.sstatic.net/dATiX.jpg)
> **Comments:**
> **username_0** (2014-08-07): +1 Nice find. But then why would non-rubber, like Smoker and Vergo, people turn black when they use Haki?  
> **username_3** (2014-08-14): I always assumed the black coloring was just to give the audience something to identify a "haki punch". Since the whole haki thing is only properly explained during the 2y gap, it makes sense to start differentiating visually between normal and haki attacks from that point on (with maybe some subtle hinting beforehand?).  
> **username_2** (2015-05-03): @TAAPSogeking Luffy is the main character, and he is rubber, so Oda must have focussed his thoughts more on what Luffy's Haki would look like. Then he decided that for other people's Haki, he would use the same "color coding" to keep things simple, and avoid questions like, "why does Mingo's Haki look pink?" :)  
> **username_4** (2016-10-27): @Kevin Hnestly, looking back, I think the most logical reason it was never colored in, as an IN universe kind of deal, is because none of the straw hats could detect it before. The haki Arrows that pierced stone were easily shattered in luffys hands, and he had no idea why. After the 2y time skip, they all learned how to use it, so naturally they could begin detecting it. I know more than one example of strange powers that were revealed to be invisible things. Such as YuYu Hakusho's bomber guy, and the Invisible hands from Re:Zero  
---
### Answer by username_5 on 2014-01-12. Score: 1
It depends on how dense the haki (invisible armor) they use. When garp use haki to hurt luffy, he applied just a small amount so that it doesn't really hurt or can cause serious injury. That explains alot right? When you applied a vast amount of haki on your body .. it will turn black.. because of the density of the haki you applied on it. if it is a small amount.. then it's like invisible..
---
### Answer by username_6 on 2014-08-14. Score: 1
In the pre-timeskip, use of Busoshoku Haki as "invisible armor" was shown as a swift percussion forming a light-blue beam, similar to lightning, while in the manga, it is shown simply as an amplified impact, nothing else visible is shown... from wiki :v
---
