Applying the candy over the actual chrome isn't really a problem but getting it to stick well is where the trick comes in.  First of all, you have to remember that a candy color is simply a tinted clear.  Therefore, anything underneath will show.  This eliminates our ability to use phosphates to etch because they will discolor the chrome, which WILL SHOW UP in your finished project.

   You really have two options:  Option #1 is to try and VERY lightly scuff the chrome with a scotch-brite pad.  Not my favorite choice but it seems to work most of the time.  My preferred way is to actually wash the wheel with pure ammonia.  The ammonia will etch the chrome without discoloration, so you get the best result.

Happy Coating!