Hot answers tagged layers
Open "Levels" and zoom in as close as you can on one of the incorrect pixels. Using the Black Eye Dropper within the Levels window, click on the bad pixel. It will change all pixels of that color (and darker) to pure black.
You need to work on the same layer as the circle, in this case. If you want to keep the circle for reference, then clone that layer and hide the original. Work on the cloned layer of the circle and use your eraser to punch a hole in it.
If you want to paint directly onto the Cyan channel then you should be in the Cyan channel on the panel: It should then work just fine. You can't paint on the Cyan channel of an empty layer because there is no Cyan channel.
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