i have a question: how's the transparent determined by and how many layers can use that color on his tiles?
this activity could be fun!
I don't really understand the question, but I could explain.
The Snes has a part of the graphic memory that is 512 bytes long that is devoted to colors. Each individual 16 bits represent a color. It stores up to 256 16-bit colors to be onscreen at one time. The colors are actually 15-bit (5 for red, 5 for green, 5 for blue), the last bit is just ignored. The graphic mode determines how many background layers and also how the 256 colors are divided.
In mode-0, the first 128 colors are used for background, the last 128 colors are used for sprites. The 128 background colors are divided into four parts. Each of the 4 background layers has it's own 32 colors. BG1 has colors 0-31, BG2 has colors 32-63, BG3 has colors 64-95, BG4 has colors 96-127.
Each of the layers 32 color palettes are divided into even smaller palettes. Each layer has it's own 8 4-color palettes. Palette-1 is colors 0-3, Palette-2 is colors 4-7, Palette-3 colors 8-11, ect ect.
The first color of each 4-color palette is never shown, because that color indicates a transparent pixel. Transparent pixels are pixels that mean "go display the pixel from background layer behind it." If there is a transparent pixel in the farthest background layer, it is replaced by the background color, which is always going to be color-0 on the big 256 color palette.