Yes. You’ll need someone to make an extension or use my JavaScript Extras Extension. If you use my extension there is a Set Palette block that takes in a Buffer, basically a number array that is a certain length. There are blocks for creating buffers from number arrays, which will be easiest to understand. This buffer needs to hold the data for every color, from 0 to 15, and each color is the red green and blue values for the color, so 3 * 16 it needs to be 48 values long. Good luck! I’m on my phone so this is the most I can help right now.
no extra colors here
You can change which color each “color” actually is, but you can only have 16 colors on the screen at a time (black and the color you get when you don’t have anything on the screen are not the same color, but it would be really annoying to try to use that as an extra color in a game)