Textured brushstroke looks off when exporting with transparent bg

Hey y’all, I’m new to Harmony and I just had this problem. I need to export an animation with a transparent background so I can layer it on top of a video. I’ve managed to do that using the “Millions of colors +” setting, but only sort of. I mainly used brushstrokes with the “chalk” paper texture setting, and while they looked ok on Harmony, after exporting, they look… dirty. The points where it should be transparent (where there was no “paint” due to the texture) ended up black. So while I have a transparent BG, I don’t have a transparent brushstroke. I’m sorry if I’m not being clear, this is all very new to me. I’ve attached a pic of the video in question; the BG is transparent, but the brush looks exactly as it does in the video; with black splotches where it should be whatever BG I’d put behind it. Anyone know any way to fix this? Thank you.

EDIT: I circumvented the issue by using the pencil tool instead of the brush, but I’m still curious as to what I could’ve done to fix the original issue. Thanks again.