another way you could have done a cleaner transition without the blending of colors is to find any kind of material with small holes and use to mask it off, to get a sort of screen print effect, the colors will be more discrete yet still get the fade effect w/o as much of the browning. Alot of stuff in the 90s did this for that very reason,

need some hammer pants to go with that bike.

Did you rough-up the old paint before spraying over?