There is something off somewhere, After Effects is always RGB but you should be able to make the round trip without any noticeable quality drop. I don’t know what you’re doing in after effects but try these steps to try and narrow down the problem:
a. Bring your final cut export back into your timeline before after effects processing to make sure the export didn’t mess it up.
b. Render a clip straight from after effects without any effects or transformations to see if something is off in your project, render to 10bit and lossless animation and bring them both into final cut to see if they’re messed up. Make sure your render settings are at best quality and not current or anything else. (I always recommend setting the default to best for all outputs as one of the first changes to settings on a new box or install)
When you bring the after effect renders back into final cut do they have to render in your sequence or do they match the sequence settings.
Let me know how you get on.
Glenn Stewart
1k studios