  Vanadium dioxide ($VO_{2}$) exhibits strong infrared optical switching due to
its insulator-metal phase-transition property. However, in the visible
wavelengths, it's intrinsic optical switching is quite low. Current research
explores solutions like multilayering, intricate structural patterning, high
thermal budget processes and costly metals for improved color switching.
Nonetheless, the color gamut coverage with these methodologies remains notably
limited. This work overcomes these limitations and demonstrates dynamic
multi-colour switching covering a large color gamut using a simple,
unpatterned, ultrathin ($\sim$ $\frac{\lambda}{14}$, where wavelength $\lambda$
is taken as 575 nm at the center of visible spectrum) asymmetric
Fabry-P\'{e}rot structure of $VO_{2}$ on Aluminium (Al). We use the transfer
matrix method to design the $VO_{2}/Aluminium\,(Al)/Sapphire$ structure for
maximum visible reflectance switching. $VO_{2}$ films are synthesized using a
simple, low thermal budget atmospheric oxidation of Vanadium (V). With varying
oxidation durations, different colors of the oxidized samples are observed.
Consistent and reversible color-switching is observed visibly and in
reflectance measurements with the change in temperature from low (RT $\sim$
30$^{\circ}$C) to high (HT $\sim$ 100$^{\circ}$C) or vice versa due to the
phase transition property of the $VO_{2}$ layer in the structure. Compared to
the existing studies, this work shows a significant change in chromaticities
and covers a large color gamut when plotted on the CIE chromaticity diagram.
This work has potential applications in the fields of display, thermochromic
structures, and visible camouflage.
