To explain, the reason this didn't work is because graphics pages actually don't support every color from RGB(0,0,0) to RGB(255,255,255). Instead, the colors are rounded down to the next lowest multiple of 8, so when you set a pixel to RGB(255,70,70), it actually ends up getting set to RGB(248,64,64). (More technically, GRPs are stored in a 16-bit RGBA5551 format instead of 32-bit RGBA8888.)