Hi there,
did you ever find an answer to this? Despite what the other dude thinks, being able to sample a color with a levels or curves effect is one of the most valuable tools a compositor can have.
I’ve come from a Nuke background where sampling black and white points on a grade node is pretty much the basis of accurate color matching. Real shame there’s no equivalent in AE.
Will continue looking and post again if anything turns up.
Cheers.