Early on in my photographic career, color casts were not a big issue for me...or so I thought. The fact of the matter is, I just hadn't learned how to recognize them. Now, years later, I anticipate color casts in many situations. You may notice that if you're photographing something white on a bright sunny day but your subject is in the shade, that the white items become somewhat blue. The blue sky is being reflected off of your white subject and the camera records the blue color.
Again, if you're in a forest photographing waterfalls or perhaps a bird or bear, (I'd give the bear some space!) everything around you is green. When you get your lovely waterfall images back to your computer, if you're not looking for it, you may not notice that your water has turned a bit green as well.
So how do we deal with this?
Luckily, in the age of digital photography, we have quite a few options. But first we have to figure out how to see the color cast.
I typically bring my photos into Lightroom to do basic adjustments. You can do this technique in either Lightroom or Photoshop. Bring it into the develop module and go to the HSL sliders. Crank the saturation sliders all the way to 100%. This will show you what colors are in your image...greatly exaggerated! If there is "blue" somewhere it shouldn't be, like in a white shirt or white egret, then you have a cast there. If you have excessive yellow or green, then you have a yellow or green color cast. Look at the image below. Their shorts are supposed to be white but due to them being in the shade/shadow on a sunny afternoon, they look blue. You might not have even noticed if I hadn't said something.
Here's the image in Lightroom with some of the Saturation sliders all the way to 100%. Yup...definitely blue. And you can see blue showing up in the wooden bench that they just jumped off of. Should wood be blue? Not in my opinion.
Here we have the same image brought into Photoshop with a Hue/Saturation layer on it. I chose the "master" colors and moved the slider to 100%.
Oh My! Now I know why people say not to push the saturation slider too much. Yikes!
By doing this I've discovered areas that are blue but shouldn't be; their shorts, the writing on their shirts, the bench and deck below them.
And here's how I like to fix it. I add a saturation layer, desaturate blue and cyan, fill that layer mask with black, and paint the "lack" of color where I want. I usually choose a brush opacity of about 70% because I've found that most of the time, the things that are white end up looking too yellow when I remove 100% of the blue. And this is the result after less than a minute of tinkering. No more blue shorts, shirt, or bench. I've also retained all the blue in the sky because I used a layer mask. If you're unfamiliar with this process, I happen to have a YouTube video describing this exact process. It's a few years old from Photoshop CS5 but the process is the same. If you wish to subscribe to my YouTube Channel, Please subscribe to This One as the other is no longer being updated. You can even create an action to do this process. I created one called "Remove Blue Sky Effect" and all I have to do is play the action, paint the areas I want to remove the blue, and I'm done.
Color Casts are not always obvious. Take this image of the Angel Oak tree on Johns Island, SC. At first glance, you wouldn't think anything needed to be changed.
Another method I use to identify a color cast is with NIK Color Efex Pro4. This program has a filter in it called Pro Contrast. And though its primary purpose is to add contrast to a photo, it has a slider called "correct color cast". When I drag that slider all the way to 100%, whatever color Pro Contrast tries to make my image, the opposite is my color cast. So if it tries to add magenta, I have a green cast, if it adds blue, I have a yellow cast.
Above we see the original image in Color Efex Pro with the sliders at zero. However, when I drag the "Correct Color Cast" slider to 100%, it changes the overall color of the photo quite a bit. Suddenly, what we thought was "ok" really looks too yellow to me now. This is where I would either use the "brush" feature of Color Efex Pro4 or use Control Points in order to remove the color cast from all the branches...but I really don't mind if the leaves get a color boost here so I'll leave it.
If you're unfamiliar with Color Efex Pro4, I have an instructional video that will walk you step by step through this amazing program. Color Efex Pro Video
Here is the final image I came up with. I removed most of the color cast from the branches but left it in the leaves. It's a subtle difference but a difference I think it needed. Keep in mind, not all color casts are bad. I like to keep a "warm" cast that typically shows up during sunrise and sunset images. It's entirely up to you.