Agreed with DT.
Kecleon doesn't have the bulk to set up Nasty Plot without Substitute or something, and then that only leaves two moveslots for attacking, which is terrible, given how dependent Kecleon will be on Nasty Plot.
I'd just go with the classic SubPunch and dual Priority. You'd be surprised at how effective it really is, since people will try to exploit Color Change in order to make you look stupid, meaning they'll take a turn or two to set you up, while you hit them in the face with Fake Out, then a Focus punch or Sucker Punch.