itch.io

I see two ways:

1. you can change palette RGB values directly in the RAM by using poke api function (here are 16 colors * 3 rgb=48 bytes by 0x3FC0 address);
2. change color index in the PALETTE MAP using poke (here are 16 bytes with color indixes by 0x3FF0 addr);

64K RAM layout
--------------
0000-SCREEN
3FC0-PALETTE
3FF0-PALETTE MAP

Thanks.