Am at a loss. Have a new image which is the scan of some music. Using Magic Wand, I selected all music from paper background and created a Channel selection. On a new layer, Music layer, I did a black fill of the selected music. I then place a white layer below below it. The selection of the original music carried with it blemishes: small black marks, and a few very light gray areas. When I select a blemished area, the selections under Edit are all gray ... not active. Nor can I use the Brush tool to paint on the layer. What am I doing wrong?
Could you please post (a section of) the original image and a screenshot of the edited one with the Layers Panel visible?
Why the Magic Wand, could you not use the luminance itself?
Check the document color mode and provide more info. We don't know what version of PS on what system, what scanner and so on...