Subject says it all. IDEA is not very friendly to third party look and feels.
It seems IDEA changes the basic theme colors after the L&F is loaded, messing up with the whole color scheme. This does not causes problems with unthemeable (in the Metal Theme sense) L&F like Alloy, but makes L&F like the Plastic family (from JGoodies) unusable.
I can guess the color tweaking is necessary to make the IDEA L&F look the way you want. If this is the case, you could check if the current L&F is the IDEA L&F before making these adjustments. Or better yet, move these adjustments to the IDEA L&F initialization instead of setting then during application startup.
Maybe this has something to do with this[/url] SCR, which would also be welcome.