If you don't have a vectorscope that shows you the IRE levels you can use the not-that-secret flame spark "Broadcast" which is found in /usr/discreet/(flame version)/sparks
you can set the IRE you want it to clamp and it'll be downright evil with anything above that setting. Since you dont' want that, you put a color correct node between the clip and the spark and a differenceMatte node with the CC as one input and the spark as the other. Set the difference gain way up (1000 should be fine) and set the difference node as the context (hold the + key and tap the node). Always go into the spark, even if you change no settings. I've seen it not take effect till you 'wake it up' in that way. At this point, go back to your CC and look at your difference matte. Drop the saturation in the highlights and possibly bring the gain on them down until you've got no difference in the two images and viola! broadcast legal color.
There's some other cool things in the /usr/discreet/(flame version/ directory. I use the basic 3d primitives from the "models" directory all the time, and there's pre-made gmask shapes and other useful sparks.