The number of colors is supported by the graphics card. The more colors you use, the better the image quality, but the higher the processing requirements on your system.
Each pixel is specified by a specified number of bits. True Color (24-bit Color) supports 16,777,216 colors and High Color (16-bits) supports 65,536 Colors. If it is less than 16-bits color, the image will not look good. Most drivers do not offer 8-bit (256 Colors) or 16-bit (32,536 Colors) settings. Newer PCs support 32-bit color, adding 16 million colors as True Color. There is little that can be done to help.