(from Rackme32)
Photoshop... In my 20+ years of computer play, I have never gained any interest, and haven't even had any version of it on any of my computers for at least 10 years.
Is Photoshop knowledge necessary to do CourseForge, or is it used just for advanced tweaking of textures, colors, etc.?
Don't worry, you won't need Photoshop. You will get enough generic textures (with some colorisation options within CF) to manage perfectly well without it. Or without any other graphics editing software at all.
Should you be familiar or comfortable with another such software (Gimp.org), you may use that instead, no problem.
It is, as you wrote, helpful for advanced texture manipulations, but not a necessary knowledge at all.
Only a desirable one, but that's entirely your call.