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+*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.
+
+
+ vim:tw=78:ts=8:et:ft=help:norl: