Many of the AVR/STM/Arduino compatible TFT displays available can display up to 64K colors .
These screens using the RGB565 (16-bit color) specification instead of what you're used to, RGB888 (24-bit color).
The RGB565 color bitmask is rrrrrggg:gggbbbbb: red - 5 bit (0-31) in MSB, green - 6 bit (0-63), blue - 5 bit (0-31) in LSB.
For RGB888 <-> RGB565 color conversion, you can use this online color picker.
