Submix = keystone.

I've noticed that when i put L1 at 80% with RGB layerblend 10 and L2 with RGB layerblend 10 with a black.pct on it, full intensity the image at layer 1 becomes brighter.

L1 = image with text on black background with RGB arb, L2 as above, L3 as above. The text on L1 becomes crisper.

Working with this principle i've put the black.pct on the last layer (L8) and programmed the crossfades on the lightingdesk. It's always looking for good balance.

Perhaps there's a better way but i worked for me.