Lapis256 is a simple 256 colorscheme with:

• moderate contrast between background and text
• soft contrast between many common syntax elements
• lots of blue
• GUI support as of 2019 (thanks to toastal)

(C function color requires adding a custom "syn match" to .vim/after/syntax/c.vim file, or similar, then mapping to Function: "hi def link cppFuncDef Function")