I would like to make a (semi-)transparent brush in GIMP.
Starting from an image of marble with white background and veins in shades of grey, using various layers I selected the white to alpha and then changed the Hue, so now I have nice red veins on a transparent layer. I would like to turn this transparent layer with the red veins into a brush.
However, whatever I try, the brush has a white background colour (even when I delete all other layers).
I just want the veins on the brush, no background colour. Is there any way to retain the transparency while creating the brush?