How to adjust color of custom brush in texture paint mode? (issues with color ramp) I have an image where the brush part is black and the background is white.

After I loaded the custom brush in texture paint mode, I thought that I could adjust the brush color and background color using the color ramp in the textures menu (image below).

From how I understand it, I thought that the color ramp would map blacker values in the image to the tick color on the left, and whiter values to the tick color on the right.

So to test this, I tried setting the left tick as black with 1 alpha, and the right tick as white with 0 alpha. But then the brush draws nothing. Sliding the left tick around did not help. (What I expected was that the brush part would draw black, and the background would be transparent.)

What am I misunderstanding?

My end goal is to adjust the color of the custom brush (for example, toggle between black and white, like with the default brushes) within texture paint mode whenever I want, without having to edit the brush image externally.
Black is nothing, white is full. If you want to use a color ramp, set the main value as white and the zero alpha as black, and then choose the color in the actual brush color picker in the tool bar.