Photoshop seems to have a special mode for blending spot-color channels. Let's look at an example: blending full opacity red #ff3c1f with full opacity cyan #1cd4c6.
If I create two spot-color channels with solidity 0% and set their colors to #ff3c1f and #1cd4c6 and fill them with black I get #91550D:
Now, I know that combining colors is a complex problem that's not even well-posed. But the result that photoshop gives gets very close to reality most of the time for me. Can anyone help me understand how photoshop does this blending?
I have read on the Adobe forums that it's multiplicative blending in CMYK. So I tried to reproduce that with layers, but I am getting #7D4339:
I know CMYK is device-dependent but I've tried lots of various profiles but none worked like the spot-color channels. The screenshot is from using the U.S. Web Coated (SWOP) v2 profile.
I tried Multiply blend in Lab and in RGB, but those were even further off.
I would really appreciate any insight on this whatsoever!