Each pitch (pitch class, actually) is mapped to a color. The mapping is more or less arbitrary, subject to the constraint that the basic palette derives from some characteristic of the song being painted. The palette for "Twinkle Twinkle Little Star" was determined by taking colors from an imaginary box of crayons, since the song tends to be classified as a children's song.
In addition to establishing a mapping from pitch classes to colors, I need to determine an arrangement of the notes (shapes) on a two dimensional grid that reasonably captures the grouping structure of the melody at some level of abstraction. Here is a possibility for the bit of "Star" under consideration.
Here is an image of the "Star" painting as it hangs in the Chromesthetic Gallary, a little space in the building where I work. Something like a half dozen of my paintings are displayed there. The tryptich reflects the ABA structure of this little melody. As you allow your eyes to scan the piece, left panel to right panel, reading each panel top-down and left-to-right as you would a page in a book, sing:
