Robert, if you want a ProRes 422HQ export that looks like what you've made
don't export "Using QuickTime Conversion" -- a horrible pathway -- but instead export a "QuickTime Movie". First go into your Sequence Settings and change what it calls the "Compressor" to ProRes 422HQ. Click "Advanced..." and there make the gamma correction "None".
You omit to mention in which codec you made your edit. If it was another ProRes codec the above advice is sure to work, but if it is some wayward codec we can't be sure.
There is also a question of monitor calibration affecting different playback applications differently. Although the thing you export will look the same as the thing you edit in FCP7 when both are viewed in FCP7, some other player might make the export look different. If you use the player allied with FCP7, QuickTime Player 7, then make sure to set in its preferences "Enable Final Cut Studio color compatibility".
I am sure that the DCPs I make using "DCP-o-matic" match my edits in FCP7. For verification I've colorimetered test colors in the FCP7 canvas and then, using the same colorimeter, on the screen on which the DCP was projected. Getting there required a calibration odyssey, but the point is: it's possible.
Dennis Couzin
Berlin, Germany