That was my subconscious. 4 is the maximum, but I'd actually steer more towards 1 or 2 types when possible. If the diagram is very complex and needs more types, I'd try to split it into several slides.
I saw the slide and the "visual complexity elimination subroutine" kicked in. I'll try to fix that in a future version.
Yes, this is something I should have written explicitly. Your advice is spot on, I should have included a "conclusion" in the colors section saying just that.
I used LibreOffice Impress over Ubuntu for that presentation.
I try to use the best tool for the job though.
Two weeks ago I had to make a code-based introductory presentation and I used showoff instead ( https://github.com/schacon/showoff ) since it comes with syntax highlighting and the slides are just a text file. It took me maybe a couple hours to learn the ins and outs, but then it was easy.
I've heard that the Mac app is good, too, but I haven't used it yet.