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+1 @ think in color channels doesn't come naturally.
I thought I'd NEVER get it ... still working on it, but it is mostly like anything that takes time and repetition to learn.
In PS, there is the channels tab next to the layers tab. By turning on/off the view of the different channels, you can view the different aspects of what each channel contributes to the image.
I'd recommend looking at an image with easily defined reds and blues ... along with white. An image of the American Flag would fit the bill well here. You will be able to see the areas that are reflecting mostly red, mostly blue and both red and blue. You'll also be able to see where the green channel is / isn't relative to the red, blue and white areas.
The aspect that you'll notice that in the white portions of the flag, there are essentially equal amounts of light being reflected in all three R,G & B channels.
Again, it doesn't come naturally at first, but if you've got a Sherlock Holmes mindset as to "who dunnit" ... you'll come to figure out who the culprits are for virtually any crime scene.
Also, if you are in Channels (before you add layers, etc), you can click on the panel and an option for "Split Channels" is available (grays out once you add layers). This will create three new files ... one of each channel, but you'll have to reopen your original file if you want to have 1 color and 3 channel files open at the same time.
I find it helpful for analysis, but even more so for mask creation. Dan Margulis books on LAB or PS are both helpful, but the book Channel Chops really built upon Dan's books to where it started to "click" for me.