Color blending mode in Photoshop

Layer blending modes: too many choices
If you look at the pull-down menu in your layers palette, you will see a dizzying number of choices with names that do not make sense without explanation. If you want to know what all of those blending modes mean, several great posts out there take the time to explain each one of them:

• Northlite starts with a primer on color and then demonstrates blending modes with a leafy background and a rainbow gradient. Excellent concise explanations.
• Digital Art Form's post is not exhaustive, but it is certainly methodical.
• And speaking of methodical, check out Nathan's programming magic. This is the kind of stuff that my son just eats up. For those of us that are less skilled at programming, scroll down past the blend mode math and check out the photos. As a photographer, I appreciate how Nathan demonstrates the blend modes on photos rather than on graphics.
• Photoshop Essentials simplifies the blend modes by grouping them into five categories. Very readable.
• Adobe Press shows us "how blending modes think."

As much as I respect all of the above, I start to get vertigo when so much information is presented at once. And even though helpful people have gone through the trouble to demonstrate the effects of each and every blending mode, I am left unsure about practical use.

A book suggestion
I think that Matt Kloskowski's Layers book is the best thing out there for people like me (i.e. people who prefer not to be overwhelmed), because it focuses on the layers features you will actually use. In fact, chapter two of his book cuts the list of 25 blending modes down to the three modes he deems the most useful (multiply, screen, and soft light). That's not to say that he doesn't use other modes in the book, but simply that he keeps it practical.

My own top three blending modes are multiply, screen, and overlay (which is almost the same as soft light). But in honor of the May monthly special on "color," I decided to dedicate this post to the "color" blending mode with an emphasis on practical use in photo retouching.

Color blending mode: what it does
Let me quote Northlite's pithy definition: "Color [blending mode] changes the hue and saturation of the lower layer to the hue and saturation of the upper layer but leaves luminosity alone."

Not making sense yet? Let's look at an example. I will start with a color photo:
In the layers palette, I add a new empty layer. Just to show how the color blending mode works, I will fill that top layer with white by using the paint bucket tool with the foreground set to white.
This leaves me with a plain white screen. Next, I choose "color" from the layer blending modes.
Because the color blending mode leaves all of the shades of gray (i.e. the luminosity) intact, my white top layer blends down to create a black and white image.
Although I would recommend different methods for customized black and white conversion, the example above should help you visualize what the color blending mode changes (hue, saturation) and what it leaves alone (luminosity).

And now on to real-world use...

Toning an image with color blend mode
If you fill a new blank layer with any color (as I did with white above) and set the blending mode to "color," you will get a toned image. So this time I will use a beige color on the top layer.
The result is a nicely toned image:
This is exceptionally easy, because I go straight from color to a toned image. Change the color of the top layer, and you change the tone:

Enhance or change color selectively with the color blend mode
Two more tricks with the color blending mode start with the same steps as above, but then modify the top layer in one or both of the following ways:

1. Play with the opacity
If you lower the opacity of the top layer, your background color will start to come through. This can look very ugly at 60%, but can be very useful at 15% to either add or correct a color cast. In the photo below, I applied a yellow layer at about 20% in the color blending mode. The right half shows the new warmer version, and the left half is the original more ruddy complexion. Just to make sure you could see a difference, I set the opacity higher than my ideal.
2. Color blend + layer mask = selective color change.
Add a layer mask to a toned image, and then paint color in or out. I usually prefer to paint in rather than out, so I add a layer mask filled with black by clicking the layer mask icon while holding the alt key.
Now I can use a white brush (b) on the mask to paint in color selectively. If blue is my top color, and I mask out everything except the eyes, I end up with...
AAARRRGHHH! Ridiculously fake bright blue eyes!!!! But if I dial down the opacity, I get a realistic change:
Or I can do the same thing to shift his hazel eyes more toward green:
Since the color blending mode leaves the luminosity alone, you get all of the shading of the original image. Even the super intense blue might be believable if more people in the world had the eyes of Paul Newman. Back to the real world...In my own work, I never have any reason to change hazel eyes to blue or green, but I might want to enhance a person's actual eye color if a photo didn't do it justice.

In the end, our only potential obstacle to realistic color manipulation is self-restraint (the lack thereof). But then again, who says realism has to be the goal? Start to experiment with the color blend mode and you will appreciate its ability to create highly stylized effects.