https://tonsky.me/blog/syntax-highlighting/
@nikitonsky convinced me that the highlighting is colorful but useless the way people usually do it, but I never spend time tweaking any themes since then.
Until this week.
I started with Solarized colors and styling all text the same and then made comments stand out and some declarations and function calls. Xcode can't do much more than than. We can't have background colors, either. And I don't see as many colors (deuteranopia), so it's a reduced palette :)