I think you almost answered your own question there. No tooltip for the actual canvas layer, but there is one for the "+" button above it, and that would be what you're looking for. Maybe I should add a tooltip for the actual layer "rectangle" as well.
Remember to check readme.txt for information on "all" features. It's a bit clumsy and short at the moment, but I'll make some kind of html documentation with images later.
I've tried making a few example images for color profiles in general, but it's kind of hard to find a good static scene that explains it clearly. If you want to compare them yourself, you can paint a few patterns using different colors on the bottom layer, then create a new layer and paint some large blurry strokes there using a few other colors. If you switch the color profile at this point, the hovering layer will blend differently with what's beneath.