Most of the time, the window is about 24-48 hours. Since most basecoats, don't have hardeners in them, the new "flames" basecoat shouldn't have any problem "biting" into the original basecoat. If it goes over this, usually I just use an adhesion promoter.
Spraying purple over black is an excellent choice, as long as it is a metallic, pearl...if it is a solid purple (non-metallic or pearl), I would suggest a very light gray or even a white if you want a brighter purple.
All the panels on my truck were painted with a black sealer, then sprayed with a purple pearl (my own mix in Glasurit paint) over it.
<center><img src ="http://www.e-partssource.com/personal/1963chevy/digital/rear_shot_sm.jpg" border=2></center>
See more on my truck
here
Enjoy!
Scott F
