The diagnosis is valid but the prescription is incorrect.

The solution is not to use fewer colors, but rather to take advantage of the 3D space of color perception.

Good themes have a hierarchy. Perhaps red is for keywords and blue is for symbols, but different kinds of symbols have different shades of blue. A lighter blue for functions, a darker blue for classes, for example.

This allows the highlighting to convey a higher amount of information when reading code closely, without causing distraction when skimming through code.