diff --git a/docs/web-ui/css-vars.md b/docs/web-ui/css-vars.md
index fa17eaaa..a7d42f22 100644
--- a/docs/web-ui/css-vars.md
+++ b/docs/web-ui/css-vars.md
@@ -17,6 +17,19 @@ reference the **semantic** names and must **not** redeclare them or reach
 for the raw `--baseNN` slots directly. (`base.css` holds only the shared
 `body` typography — it references the palette but no longer defines it.)
 
+`colors.css` ships two rows of the same 16 slots: an unconditional
+Catppuccin Mocha (dark) default, and a Catppuccin-Latte-derived (light)
+row gated behind `@media (prefers-color-scheme: light)` — both use the
+identical slot mapping, so which row is active never changes what a slot
+means. The light row's `base00`-`base07` (surfaces/foreground) are stock
+Latte hexes; `base08`-`base0F` (the eight chromatic slots) are darkened
+from stock Latte to actually clear WCAG AA against how this app uses
+them (real contrast failures found in review — see the comment above
+those declarations in `colors.css` for the numbers and why). This is the
+OS/browser-level default only; it's what a client with no more specific
+theme decision gets (see "Theme swapping" below for how a stylix
+deployment or a future per-user override supersede it).
+
 Both are deliberately standalone, not `@import`ed into the page bundles:
 each package re-exports them (`src/{colors,theme}.css` →
 `@import "@hive/shared/…"`) so esbuild emits its own
@@ -114,7 +127,14 @@ to `theme.css` (the "Derives from" column above) — a generator never
 needs to know our var names, and `theme.css` + the page bundles stay
 untouched.
 
-`colors.css` base16 slot defaults (Catppuccin Mocha):
+**Two rows, one contract.** `colors.css` ships both a dark default
+(Catppuccin Mocha, unconditional) and a light default (Catppuccin Latte,
+behind `@media (prefers-color-scheme: light)`) — a theme generator that
+overrides the file wholesale (e.g. the stylix path, which writes a single
+unconditional `:root` block with no media query) supersedes both rows at
+once, same as today.
+
+`colors.css` base16 slot defaults (Catppuccin Mocha, dark default):
 
 | Slot     | Default   | Standard base16 role | Mapped to                                           |
 | -------- | --------- | -------------------- | --------------------------------------------------- |
diff --git a/frontend/packages/shared/src/colors.css b/frontend/packages/shared/src/colors.css
index 3fa8ca51..25181d13 100644
--- a/frontend/packages/shared/src/colors.css
+++ b/frontend/packages/shared/src/colors.css
@@ -29,3 +29,71 @@
   --base0E: #cba6f7; /* magenta / mauve */
   --base0F: #f5c2e7; /* extra accent — pink */
 }
+
+/* Light-mode default. base00-07 (surfaces/foreground) are stock
+   Catppuccin Latte — no contrast issue there, they're the ends of the
+   bg/fg scale. base08-0F (the eight chromatic "tone" slots: red through
+   pink) are deliberately NOT stock Latte hexes — see the comment right
+   above those declarations below for why; don't reuse stock Catppuccin
+   Latte's own accent hexes there if this ever gets regenerated.
+
+   This is a *default*, not a user preference store: it only applies
+   when nothing more specific has already decided the palette. A
+   stylix-generated colors.css (nix/host-modules/hive-c0re/theme.nix)
+   replaces this entire file wholesale — a fixed, unconditional `:root`
+   block with no media query in it at all — so a stylix-themed
+   deployment is naturally unaffected by, and never fights, this block.
+   Some people need light for low-vision/contrast reasons, others need
+   dark for photosensitivity, so respect the OS/browser signal by
+   default the same way `prefers-reduced-motion` already is elsewhere —
+   rather than always forcing the bundled dark palette on a client with
+   no stylix session of its own (e.g. a phone browser hitting swarm-ui
+   directly). A future per-user override takes precedence over this
+   media query by simply setting the vars later in the cascade (e.g.
+   via an inline `style` on `:root`, which always outranks a
+   stylesheet rule). */
+@media (prefers-color-scheme: light) {
+  :root {
+    --base00: #eff1f5; /* default bg */
+    --base01: #e6e9ef; /* lighter bg (elevated surfaces) */
+    --base02: #ccd0da; /* selection / surface — borders */
+    --base03: #bcc0cc; /* comments / dim surface */
+    --base04: #acb0be; /* dark foreground */
+    --base05: #4c4f69; /* default foreground */
+    --base06: #dc8a78; /* light foreground */
+    --base07: #7287fd; /* lightest */
+    /* base08-0F: darkened from stock Catppuccin Latte's own accent
+       hexes (same hue/saturation, lower HSL lightness), not a literal
+       upstream port like base00-07 above. argus's review on this PR
+       computed real WCAG contrast ratios and found the literal Latte
+       accents fail badly as `StatusChip` fill-text (green/amber/red/
+       yellow on `--purple-dim`/base03: 1.4:1-3:1, need 4.5:1) and even
+       as plain text on `--bg`/base00 in the agent/dashboard packages
+       that also consume this same file (2.3:1-4.8:1). Root cause:
+       Latte's own accent colors are calibrated against Latte's
+       near-white `base`/`crust`, not against a mid-gray `surface1` —
+       the Mocha row doesn't have this problem because Mocha's pastel
+       accents are already *light*, so they contrast fine against a
+       *dark* surface1; Latte's saturated-but-mid-brightness accents
+       don't have the equivalent headroom against Latte's own
+       (much lighter) surface1. Each value below was picked by holding
+       the stock Latte hue+saturation fixed and binary-searching HSL
+       lightness down to the point real contrast against base03 clears
+       4.5:1 with a small margin (also verified against base00: all
+       land above 7:1 there) — same hue identity, same base16 role,
+       just dark/saturated enough to actually be legible as filled-chip
+       or plain text either way. Yellow and peach read closer to
+       olive/brown than a bright yellow/orange once darkened this far —
+       an inherent property of darkening a warm hue in sRGB (Bezold-
+       Brücke shift), not a mapping mistake; boosting saturation
+       further didn't rescue it (verified). */
+    --base08: #9c0b2a; /* red */
+    --base09: #883201; /* orange / peach */
+    --base0A: #6d450e; /* yellow */
+    --base0B: #235818; /* green */
+    --base0C: #025374; /* cyan (our sky — note: Catppuccin's base0C is teal) */
+    --base0D: #0843b8; /* blue */
+    --base0E: #6311ce; /* magenta / mauve */
+    --base0F: #8f166e; /* extra accent — pink */
+  }
+}