As with any task, when you’re first teaching a new subject, always pair the label with the item. It’s going to take time before the child can say the name of the color, so stay away from asking “What color is it?”.
Check the level of the child. Start by matching the colors. As the child matches, label it for them. I like to use the phrase “Match, blue with blue” etc.
If the child is not able to match independently, set up a positional prompt to increase the chances of getting the answer correct. Praise! Praise! Praise!
Learning is suppose to be fun. If the task is too hard, the child will get frustrated and probably won’t want to do it again. Keep it simple. It might not click right away, and that’s ok!! Just keep practicing!