Syntax highlighting gains, regardless of color scheme, are not negligible. There are grayscale color schemes, for example, that remove the violent nature of some color themes.
I use a custom grayscale theme in Neovim with 3 light and 3 dark colors. Comments are darkest, language syntax like keywords and brackets are normal, and assigned values bright. This helps me focus on what's important and ignore the boilerplate around. Everything is still readable but I can parse the code by just taking a glance at the relevant stuff.