I'm trying to do an additive overlay with 3 maps/colors. I'm having a lot of trouble viewing the overlap for all three maps. Is this possible?

For example, I've tried using 3warm and 4cool, which have a nice, clear light pink overlay. When I add a third overlay with blue, it doesn't seem to show the overlap at all on the 3 warm, and there's no difference (at least not that I can see) between the 3warm/4cool overlay and the 3-way overlay. I thought maybe this has to do with it being in a different color group from the other 2, so I tried 1hot (instead of blue), which seems to work a little better but still doesn't really overlay on the 3warm (2 cold is worse).

I know that if, for example, I used red, blue, and green and set the scale to wash out any gradient, the 2-way and 3-way overlays are really clear. But then this is potentially problematic because I lose the gradient, which is informative.

I'd be interested to hear if anyone has encountered this issue or found a good solution for overlaying 3 maps.