It's not you buddy, it's the tracks.
I love blue, and green, they're my fave colors. But in the game, the track palettes screw it all up.
What I do is paint a cool color, try it in game on tracks, if it turns green, I repaint it starting with that bright blue, and slowly try tinting it till it looks what I was after.
Sometimes it works, most times not, but you'll get lucky. Take my Keystone Krusher replica, that blue on there, on most tracks, it should turn green, but it always stays some sort of shade of blue. I got lucky on that one.
Dat's my best advice. If you like it to look a certain way, either try some new painting techniques, or some new shades, or delete the tracks that always mess it up.