Random Density Map GIMP Script

[Gartog, the Gullible]

...

All my gimp tree brushes are coloured image hoses, so they can be transparent with solid backgrounds[my emphasis]. Even the B&W outline ones I make are full colour[my emp.], with the outline (black) and the tree fill (white) so they will overlap without showing through[my emp.].

-Rob A>

Could someone please be elucidate?

In particular (where to start?),
* well, when is a brush wanted to be transparent(?) with solid backgrounds? (Forgive me, I don't even know if this means the brush has a solid background or that it is transparent when used on solid backgrounds)
* and how making them in color [defining the the GIMP .xcf project file using a colour palette?] effects that behavior, as compared to using black-and-white
* and regarding the "B&W outline ones," does this refer to a white tree on a solid black background (defined in a color project) or a white-tree-with-a-(narrow)-black outline on a transparent background

I apologize for my denseness, but thank you for your forthcomingness.

Gart