[Steven Quan] “Why are there two droppers for every circle? “
One is the Complimentary Color (-) and the other is the Adjustment Color (+). The Complimentary Color will select the color that is opposite the color you are choosing with the eye dropper. The Adjustment Color will select the same color on the color wheel that you are choosing with the eye dropper.
[Steven Quan] “Am I supposed to click on both droppers and do color correction for each?”
No. For color correcting (i.e., making a correction to the color you select) you want to only use the Complimentary Color eye droppers. For High you want to select a color that should be white. For Mid you want to select a color that should be gray. For Low you want to select a color that should be black. Usually finding white and black is fairly easy but there may be no gray in your image so you need to choose a color that, if the image was converted to black & white, should look gray.
~jr
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