highlight function arguments, function type signatures, and enum members

[quantum-booty]

Could we add highlights to function arguments, function type signatures, and enum members, so that input and enum members are highlighted?
I understand this may add colours that are not in the carbon colourscheme, however I think it would improve the syntax highlighting.

Function argument "input" is highlighted in Kanagawa, but not in oxocarbon.
Kanagawa:

Also, the type annotation &str in the function signature isn't highlighted in oxocarbon.
Oxocarbon:

Enum members Up, Down, Left, Right are highlighted in Kanagawa, but not in oxocarbon:
Kanagawa:

Oxocarbon:

[shaunsingh]

I'll definitely look into adding this. The original IBM theme keeps it quite simple, highlighting the bare necessities, but I agree with you in that adding a few highlights would certainly make the code easier to read.