Solid Color Layer affects entire background rather than just the brush. Clipping Mask not working!

Before converting the duplicate channel to a selection make sure you use the curves as shown. What was previously white you want totally black and vice versa. So left point up from bottom to top and right point down from top to bottom. Then move the left point to the right to increase contrast until it reaches the histogram on the curve.

Then , and only then, turn it into a selection.

That way the black areas will not be selected and will not be filled on the new layer, leaving only the brush stroke.

Dave

Hi

Add your new empty layer

Click on the mask for the fill layer and in channels panel right click and duplicate the mask channel

Select the duplicated channel and use Image > Adjustments > curves to Invert it and increase the contrast (move end points as shown)

Go to the new empty layer and select it in the layers panel.

In the channels panel select the Mask copy and click on load channel as selection

Click on the RGB channel then Shift+F5 to fill the selection with colour ( I used black)

Add your new color fill and clip it to the layer with the black brush strokes

Dave

You are clipping the layer to the solid colour below, so it will clip to the entire layer (except where you brush in full black on the mask).

Rearrange your layers as below to put the brush strokes on a separate layer:

Dave