Ever since I've been messing around with photo and video editing software, compositing or blend modes have always been confusing. I recently found this video, which is actually a part of a very well done series, and Andrew Devis, the creator, does an amazing job of explaining what the modes do. I found it really helpful how he explains how the name of mode explains what it does mathematically, and finally it makes a lot of sense. For instance, when you have the Add mode, well, adding Black to something doesn't change anything because the RGB for black is 0,0,0 whereas white @ 255.255.255 will have an effect. Any way, just sharing this because I found it to be the best video ever on the subject.