Searching for color list that unity can read from an image

Hello there my friends I’m searching for a way to know how many and what colors that unity editor can read from an external file let’s say an image of low dimensions ( 125x125 ) . I’m trying to generate a map with prefabs and all helped by an image i provide but many colors the editor don’t recognize or ignore .
so anyone can help me by documents , explanation of the problem anything helps . For my part i was testing color by color but that method is dull and take too much time I tester over 1000 color and I’m sure thousands more exists so help me out folks.

Assuming an R8G8B8 image format, it should be able to read any rgb that’s 0-255, 0-255, 0-255 without issue. I’m not so sure reading colours from an image is the ideal solution for loading however – if you really want to paint your levels pixel by pixel in an image editor, I’d load the image and convert it to more meaningful data inside the editor and save that for loading at runtime though.