*dev_theme.txt*          Nvim


                            NVIM REFERENCE MANUAL


Nvim theme style guide                                        *dev-theme*

This is style guide for developers working on Nvim's default color scheme.

License: CC-By 3.0 https://creativecommons.org/licenses/by/3.0/

                                      Type |gO| to see the table of contents.

==============================================================================
Design

- Be "Neovim branded", i.e. have mostly "green-blue" feel plus one or two
  colors reserved for very occasional user attention.

- Be oriented for 'termguicolors' (true colors) while being extra minimal for
  'notermguicolors' (16 colors) as fallback.

- Be accessible, i.e. have high enough contrast ratio (as defined in
  https://www.w3.org/TR/2008/REC-WCAG20-20081211/#contrast-ratiodef).
  This means to have value at least 7 for |hl-Normal| and 4.5 for some common
  cases (|hl-Visual|, `Comment` with set 'cursorline', colored syntax, `Diff*`,
  |hl-Search|).

- Be suitable for dark and light backgrounds via exchange of dark and light
  palettes.

- Be usable, i.e. provide enough visual feedback for common objects.


==============================================================================
Palettes

- There are two separate palettes: dark and light. They all contain the same
  set of colors exported as `NvimDark*` and `NvimLight*` colors respectively.

- The dark palette is used for background in the dark color scheme and for
  foreground in the light color scheme; and vice versa. This introduces
  recognizable visual system without too standing out.

- Actual computation of palettes should be done in a perceptually uniform
  color space. Oklch is a good choice.

- Each palette has the following colors (descriptions are for dark background;
  reverse for light one):

    - Four shades of colored "cold" greys for general UI.

        - Dark ones (from darkest to lightest) are reserved as background for
          |hl-NormalFloat| (considered as "black"), |hl-Normal| (background),
          |hl-CursorLine|, |hl-Visual|.

        - Light ones (also from darkest to lightest) are reserved for
          `Comment`, |hl-StatusLine|/|hl-TabLine|, |hl-Normal| (foreground),
          and color considered as "white".

- Six colors to provide enough terminal colors: red, yellow, green, cyan,
  blue, magenta.
  They should have (reasonably) similar lightness and chroma to make them
  visually coherent. Lightness should be as equal to the palette's basic grey
  (which is used for |hl-Normal|) as possible. They should have (reasonably)
  different hues to make them visually separable.

- For 16 colors:

    - Greys are not used and are replaced with the foreground and background
      colors of the terminal emulator.

    - Non-grey colors fall back to terminal colors as ordered in ANSI codes
      (https://en.wikipedia.org/wiki/ANSI_escape_code#3-bit_and_4-bit),
      that is red (1, 9), green (2, 10), yellow (3, 11), blue (4, 12),
      magenta (5, 13), cyan (6, 14).
      To increase contrast, colors 1-6 are used for light background and 9-14
      for dark background.


==============================================================================
Highlight groups

Use:

- Grey shades for general UI according to their design.

- Bold text for keywords (`Statement` highlight group). This is an important
  choice to increase accessibility for people with color deficiencies, as it
  doesn't rely on actual color.

- Green for strings, |hl-DiffAdd| (as background), |hl-DiagnosticOk|, and some
  minor text UI elements.

- Cyan as main syntax color, i.e. for function usage (`Function` highlight
  group), |hl-DiffText|, |hl-DiagnosticInfo|, and some minor text UI elements.

- Red to generally mean high user attention, i.e. errors; in particular for
  |hl-ErrorMsg|, |hl-DiffDelete|, |hl-DiagnosticError|.

- Yellow very sparingly to mean mild user attention, i.e. warnings. That is,
  |hl-DiagnosticWarn| and |hl-WarningMsg|.

- Blue very sparingly as |hl-DiagnosticHint| and some additional important
  syntax group (like `Identifier`).

- Magenta very carefully (if at all).

In case of 16 colors:

- Rely on the assumption "Background color can be used as background; other
  colors can be used as foreground". This means that in any
  foreground/background combination there should be background and one
  non-background color.

- Use 0 (black) or 15 (bright white) as foreground for non-grey background,
  depending on whether normal background is light or dark.


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