Make sure you remove those black bars used for Blu-ray compliance when you grade the final version because the black color will vary throughout the film if you don’t and it will be very distracting.
With a single pass regrade, wouldn’t the colour of the black bars be changed in the same way throughout the film? This is under the possibly flawed assumption that such a regrade is simply mapping RGB levels (or equivalent) in precisely the same way for each frame. It may well be more complex than that, and if the black level does vary, I agree with Clutchins that this would be distracting. In this case, would it be possible to add proper black bars after the regrade in order to make a Blu-ray compatible ISO like the original grindhouse?
I’m loving the improved colours seen so far in this thread!
Bluto