For my taste the inpainting brush tool is not visible enough working on greyscale images, because it is grey on grey and sometimes hard to see. So I would like to see the red colour of the brush even in greyscale mode.
Scenario:
Open an image. Add "Black and white" adjustment layer.
Select Inpainting brush, try to inpaint on the image.
The brush strokes color is not red, as usual, but dark-gray, as if the adjustment layer applied to it as well.