paint/spray job gone wrong

Sounds tough,
You might want to slowly work at the 'yellow' with a cotton swab and some thinner? The other alternative is to mask off the blue and just sand down the yellow until your back to a nice smooth surface (get rid of paint runs, etc.). You don't have to go right to the plastic, just enough to ge rid of any surface problems. Then re-prime (for a uniform base coat) and repaint the yellow.

Other than that, you might be best off stripping the whole thing and starting over.

M.