What is the best C++ compiler for MorphOS? Ideally an IDE with code colouring would be ideal, but not essential. I've searched Aminet for "C++" but most of the results I found were "experimental" or "untested". Which is the best?
You should get the official SDK from
mdc (requires free registration), it comes with gcc and syntax highlighting text editor. You might want to consider buying Cubic IDE aswell.
I'm going to have a bash at porting an OpenGL game to MorphOS. I assume the TinyGL library is what I want for this? I tried compiling the game under MacOnLinux and it fell over at commands like "SetColor", "SetAlpha" etc. I now know this is because OpenGL doesn't work under MOL. I assume there are equivalent commands in TinyGL?
Those don't sound like OpenGL functions at all. In fact all (or at least most) OpenGL function calls begin with gl-prefix, like glColor4f() etc.
Those sound like some internal functions of the game you're compiling, or functions from something it needs, but you don't have.