Multiblend alters transparent background

In your example, the Layer 1 Color is R = 0, G = 0, B = 252,96 and A = 0. Without correct alpha scaled output, the background RGB is passed on through even with zero alpha.

FF doesn't implement alpha blending correctly, and this is why "magical" colors reappear up the stream sometimes when alpha is raised from zero. I've spend alot of time trying to convince them to change it but to no avail. Go nudge Vlad in this discussion

https://filterforge.com/forum/read.php...MID=130993

In that discussion I also provide a lua script with correct blending. The algorithm used there is the same as in Photoshop and the one listed: https://en.wikipedia.org/wiki/Alpha_co...a_blending