I realized that I have tended, from my earliest songs, to make the main melody notes the 9th degree of the chord. So if I start the song on D min, say, the note will be an E. This might be why all my songs have the same distinctive tonality to them. It's kind of a cheap trick, but I'll take it.
I was reading a book about Duke Ellington that emphasized his use of color. It is called The Ellington Century by David Schiff. I recommend it. I am increasingly drawn to music that has that visual, chromatic quality to it. Ellington and Strayhorn, Bill Evans & Gil Evans. Of course, everything has a color, even non-chromatic music. That color is just different.