Question

When, for example, making a colorscheme, how can one define #40ffff as “UglyColor” (i.e. as a variable) ?

Possible / not possible ?

Answer 1

It’s not possible with the built in syntax. However, it can be done if the you make your own syntax:

let UglyColor = '#40ffff'
let Greenish  = '#00dd00'
let MyStyle   = 'bold'
exe 'hi Keyword gui=' . MyStyle . ' guifg=' . UglyColor
exe 'hi Comment guifg=' . Greenish

You could then take this further by creating a dictionary:

let UglyColor = '#40ffff'
let Greenish  = '#00dd00'
let ColourAssignment = {}
let ColourAssignment['Keyword'] = {"GUIFG": UglyColor, "GUI": "Bold"}
let ColourAssignment['Comment'] = {"GUIFG": Greenish}

And then process it with something like this:

for key in keys(ColourAssignment)
    let s:colours = ColourAssignment[key]
    if has_key(s:colours, 'GUI')
        let gui = s:colours['GUI']
    else
        let gui='NONE'
    endif
    if has_key(s:colours, 'GUIFG')
        let guifg = s:colours['GUIFG']
    else
        let guifg='NONE'
    endif
    if has_key(s:colours, 'GUIBG')
        let guibg = s:colours['GUIBG']
    else
        let guibg='NONE'
    endif
    if key =~ '^\k*$'
        execute "hi ".key." term=".term." cterm=".cterm." gui=".gui." ctermfg=".ctermfg." guifg=".guifg." ctermbg=".ctermbg." guibg=".guibg." guisp=".guisp
    endif

This is how my Bandit colour scheme works (with a bit more logic in there for auto-generating cterm colours, light background colours and a syntax file so that the colour scheme self-highlights). Feel free to have a look at that one and steal the functions and format for your own colour scheme.