diff --git a/HellionChat/Ui/StyleEngine/Widgets/PopupRow.cs b/HellionChat/Ui/StyleEngine/Widgets/PopupRow.cs
index c502462..ba8a6ef 100644
--- a/HellionChat/Ui/StyleEngine/Widgets/PopupRow.cs
+++ b/HellionChat/Ui/StyleEngine/Widgets/PopupRow.cs
@@ -64,8 +64,10 @@ internal static class PopupRow
                 accentAbgr
             );
 
-        var textAbgr = ColourUtil.RgbaToAbgr(
-            ColourUtil.EnsureContrast(c.TextPrimary, c.ChildBg, 4.5f)
+        var textAbgr = ColourUtil.EnsureContrast(
+            ColourUtil.RgbaToAbgr(c.TextPrimary),
+            ColourUtil.RgbaToAbgr(c.ChildBg),
+            4.5f
         );
         if (active || amount > 0f)
             textAbgr = ColourUtil.Lerp(textAbgr, accentAbgr, active ? 0.6f : amount * 0.4f);
diff --git a/HellionChat/Ui/Windows/InputBarLabWindow.cs b/HellionChat/Ui/Windows/InputBarLabWindow.cs
index b9a8f4c..17f8f52 100644
--- a/HellionChat/Ui/Windows/InputBarLabWindow.cs
+++ b/HellionChat/Ui/Windows/InputBarLabWindow.cs
@@ -178,8 +178,10 @@ internal sealed class InputBarLabWindow : Window
         {
             var glyph = icon.ToIconString();
             var size = ImGui.CalcTextSize(glyph);
-            var tint = ColourUtil.RgbaToAbgr(
-                ColourUtil.EnsureContrast(c.TextPrimary, c.ChildBg, 4.5f)
+            var tint = ColourUtil.EnsureContrast(
+                ColourUtil.RgbaToAbgr(c.TextPrimary),
+                ColourUtil.RgbaToAbgr(c.ChildBg),
+                4.5f
             );
             if (amount > 0f)
                 tint = ColourUtil.Lerp(tint, accent, amount);
@@ -286,7 +288,11 @@ internal sealed class InputBarLabWindow : Window
                 break;
         }
 
-        var ink = ColourUtil.RgbaToAbgr(ColourUtil.EnsureContrast(c.WindowBg, c.Accent, 4.5f));
+        var ink = ColourUtil.EnsureContrast(
+            ColourUtil.RgbaToAbgr(c.WindowBg),
+            ColourUtil.RgbaToAbgr(c.Accent),
+            4.5f
+        );
         using (fonts.FontAwesome.Push())
         {
             var arrow = FontAwesomeIcon.ArrowRight.ToIconString();
@@ -333,7 +339,11 @@ internal sealed class InputBarLabWindow : Window
         var max = origin + new Vector2(width, height);
         var dl = ImGui.GetWindowDrawList();
 
-        var accent = ColourUtil.RgbaToAbgr(ColourUtil.EnsureContrast(c.Accent, c.ChildBg, 4.5f));
+        var accent = ColourUtil.EnsureContrast(
+            ColourUtil.RgbaToAbgr(c.Accent),
+            ColourUtil.RgbaToAbgr(c.ChildBg),
+            4.5f
+        );
 
         // The band variant is the one the mockup drew and v1.11.0 abandoned.
         // Here at a fraction of the strength, as a tint rather than a plate --
@@ -388,7 +398,11 @@ internal sealed class InputBarLabWindow : Window
         var width = dl.DrawTrackedText(
             pos,
             text,
-            ColourUtil.RgbaToAbgr(ColourUtil.EnsureContrast(c.TextMuted, c.WindowBg, 4.5f)),
+            ColourUtil.EnsureContrast(
+                ColourUtil.RgbaToAbgr(c.TextMuted),
+                ColourUtil.RgbaToAbgr(c.WindowBg),
+                4.5f
+            ),
             1.6f * Metrics.Scale
         );
 
diff --git a/scripts/preflight.sh b/scripts/preflight.sh
index 1eb618f..af60f19 100755
--- a/scripts/preflight.sh
+++ b/scripts/preflight.sh
@@ -18,6 +18,9 @@ echo "==> preflight: Block B — manifest shape"
 echo "==> preflight: Block C — changelog sync"
 ./scripts/verify-changelog-sync.sh
 
+echo "==> preflight: Block G — colour channel audit"
+./scripts/verify-colour-channels.sh
+
 echo "==> preflight: Block D — plugin compile health"
 dotnet build HellionChat/HellionChat.csproj --configuration Release --nologo --verbosity quiet
 
diff --git a/scripts/verify-colour-channels.sh b/scripts/verify-colour-channels.sh
new file mode 100755
index 0000000..9bf6b92
--- /dev/null
+++ b/scripts/verify-colour-channels.sh
@@ -0,0 +1,60 @@
+#!/usr/bin/env bash
+# verify-colour-channels.sh — Block G of preflight.
+#
+# EnsureContrast works in ABGR. ThemeColors fields are RGBA. Feeding one into
+# the other swaps red and blue on both arguments, measures a contrast between
+# two colours that are never on screen, and returns a value in the wrong order
+# on top — and because RgbaToAbgr is an involution, a stray extra conversion
+# around the call makes it LOOK plausible while being wrong.
+#
+# This happened four times on 2026-08-19 alone (channel header, ghost buttons,
+# pill text, popup rows), each found only by a human staring at an unreadable
+# window. The compiler cannot catch it — both layouts are uint. This script
+# catches the one shape every occurrence shared: a raw ThemeColors member as a
+# direct argument to EnsureContrast.
+#
+# Legitimate calls convert first (RgbaToAbgr(...)) or pass values that are
+# already ABGR (fields/locals named *Abgr, palette.Abgr(...)).
+
+set -euo pipefail
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+
+fail() { echo "verify-colour-channels: FAIL — $1" >&2; exit 1; }
+ok()   { echo "verify-colour-channels: OK — $1"; }
+
+HITS="$(python3 - "$ROOT/HellionChat" <<'PY'
+import re
+import sys
+from pathlib import Path
+
+root = Path(sys.argv[1])
+# A ThemeColors member (via any local alias) fed straight into EnsureContrast,
+# in either argument position, spanning line breaks. Members already in ABGR
+# end in "Abgr" and are exempt.
+pattern = re.compile(
+    r"EnsureContrast\(\s*"
+    r"(?:[A-Za-z_][\w.]*\.)?(?:Colors|c|colors)\.(?!\w*Abgr\b)\w+\s*,"
+    r"|EnsureContrast\([^;]{0,200}?,\s*"
+    r"(?:[A-Za-z_][\w.]*\.)?(?:Colors|c|colors)\.(?!\w*Abgr\b)\w+\s*[,)]",
+    re.S,
+)
+
+hits = []
+for f in root.rglob("*.cs"):
+    if "obj" in f.parts or "bin" in f.parts:
+        continue
+    text = f.read_text(encoding="utf-8")
+    for m in pattern.finditer(text):
+        line = text.count("\n", 0, m.start()) + 1
+        hits.append(f"{f.relative_to(root.parent)}:{line}")
+
+print("\n".join(hits))
+PY
+)"
+
+if [ -n "$HITS" ]; then
+  fail "raw ThemeColors member fed into EnsureContrast (expects ABGR — wrap in RgbaToAbgr):
+$HITS"
+fi
+
+ok "no raw RGBA theme members reach EnsureContrast"