How to estimate SRAM usage for an Arduino Mega project with 2 displays?

Currently, I'm planning a list of components to buy, and I actually want to save some money by not getting external RAM, so I'm wondering if I can make my project work with just 8K. The color depth will be "8-bit color" I guess, so the "simplest" one. I only will use 4 total plain colors (I will animate filled circle sector like so: https://i.stack.imgur.com/jwZ9k.png). And there will be shown only one color at a time on a display. But even with 8-bit color, it gives me 1281288/8=16K, could this really be so? Or maybe this will happen only if I actually use all possible 256 colors on a single screen (which I won't)?