Can't hide my intrigue when I learned about this because I knew when I was a kid that BASIC was not the only way to program the C64 and there was another mysterious way of creating programs and games that was much more powerful.

On the C64, you always have access to all of the fixed 16 colours provided by the hardware. I like working in Hires, which on the C64 is 320x200 pixels. This is divided into "chars" of 8x8 pixels and each such char can only contain two colours at any one time. This limitation provides for quite a bit of fun and challenging puzzles.