Ok. Attached are two photos. The original "untreated" photo and then another copy with a red fill layer on top of it and the opacity decreased so you can see through it. I'm going for the effecr created by the one with the red fill layer but think there might be a more professional way to do it.
I think I only want to add red.
By specific CMYK combo I mean there is a specific red swatch (0, 100, 88, 0) in CMYK that I would like to use as the red tint to the photo.
Personally I would
• create a CMYK image where all four channels are identical (basically the image in BW) via Adjustment Layers
• use a Layer with 0/100/88/0 set to Screen
That would get an image where the luminance is directly translated to percentages of that specific CMYK color.
If additional depth is desired the Layer can be kept from affecting the black channel via Advanced Blending > Channels and the black channel be adjusted via a Curves Layer.
That way one would get a three color image, but if that is not really necessary the methods preseneted by Bill Hunt and Noel Carboni may be more convenient.
Once I change the blending mode to color is there anything more I can do to play with it than opacity and fill?
There is an additional thing you could try using the Blend If sliders in the Layer Style dialog (Lyers>Layer Styles>Blending Options)....down at the bottom there are two slider rows, work on the "this Layer" and you can adjust the highlights and Shadows. The key is to make the adjustment in the slider then hold down the Option (Alt) key and split the sliders to adjust how the adjustment blends.