cterm or notermguicolors color consistency with base16-vim and base16colorspace condition

[nlambert]

Hello, and thanks for all your work on this project.

Let me start with a light confession: between ANSI, OSC 4, GUI, termguicolors, 16-color, 256-color, and the ever-growing list of terminal emulators, I'm deep in shell shock.

That said, I've spent time digging into this, and while my experience is still fresh, I wanted to raise something that may be worth your attention.

According to the README:

Base16 is an extensive collection of colorschemes built on a common architecture by Chris Kempson. The base16_vim airline theme integrates with the base16-vim plugin (https://github.com/chriskempson/base16-vim) to match the currently selected colorscheme.

With that in mind, I noticed that the base16_nord.vim file under Airline does not seem to match the base16 architecture as implemented in base16-vim. Specifically, the ANSI cterm color assignments differ from what base16-vim uses for the same Nord theme.

Here's a snippet from the current Airline theme:

let s:cterm00 = 0
let s:cterm01 = 0
let s:cterm02 = 59
let s:cterm03 = 102
let s:cterm04 = 145
let s:cterm05 = 188
let s:cterm06 = 253
let s:cterm07 = 15
let s:cterm08 = 166
let s:cterm09 = 203
let s:cterm0A = 214
let s:cterm0B = 29
let s:cterm0C = 12
let s:cterm0D = 12
let s:cterm0E = 134
let s:cterm0F = 12

And here’s a corrected version based on the values used in the base16-vim Nord theme:

let s:cterm00 = 0
let s:cterm01 = 0
let s:cterm02 = 19
let s:cterm03 = 08
let s:cterm04 = 20
let s:cterm05 = 07
let s:cterm06 = 21
let s:cterm07 = 15
let s:cterm08 = 01
let s:cterm09 = 16
let s:cterm0A = 03
let s:cterm0B = 02
let s:cterm0C = 06
let s:cterm0D = 04
let s:cterm0E = 05
let s:cterm0F = 17

In addition to that mismatch, I also noticed that this theme does not check for the base16colorspace variable, which is part of the base16-vim plugin's strategy for supporting 16-color and 256-color terminals. Typically, the plugin uses:

if exists("base16colorspace") && base16colorspace == "256"
  " use extended ANSI values
endif

This logic is important for users who haven’t enabled termguicolors but are still using a 256-color terminal. Without it, the Airline theme may use hardcoded cterm values that don't match the base16-vim mappings, leading to inconsistent color schemes.

I realize many users rely on termguicolors (which makes this issue moot in practice), but given that this is a Base16 theme, it seems appropriate to support the full range of terminals—especially since the rest of the Base16 ecosystem does.

I also checked and noticed that monokai.vim under Airline might have the same issue, so other themes could be affected too.

Would a pull request that aligns the ANSI cterm values with the base16-vim theme and includes the base16colorspace conditional be appropriate?

Thanks again for your time and for maintaining the integration.