diff --git a/specs/t27f/deck.t27 b/specs/t27f/deck.t27
index 30f3e7fdef..67fda0047b 100644
--- a/specs/t27f/deck.t27
+++ b/specs/t27f/deck.t27
@@ -16,7 +16,12 @@
 ;   - Tome's ribbons include cyan. On our map teal and cyan mean verified and published, so the
 ;     ribbons here keep to violet, magenta, pink and blue, and a test holds every ribbon colour away
 ;     from every status colour;
-;   - a portrait frame stacks the map above the card instead of beside it.
+;   - a portrait frame stacks the map above the card instead of beside it;
+;   - the backdrop is pure black, by the owner's order of 2026-10-18 to follow our brand book:
+;     the t27.ai site paints its page #000000, and the brand book (gHashTag/tri-net
+;     phone/BRANDBOOK.md) says black surfaces, colour only as a signal, never as decoration. So
+;     the aurora ribbons are kept as colours but drawn at zero strength, and a test holds every
+;     backdrop pixel outside the map and the card at 0x000000.
 ; As in reel.t27, this file decides numbers and a host draws them: regions in permille of the
 ; frame, type sizes in pixels per preset, colours as 0xRRGGBB, opacities in permille.
 ; Contrast below is a luminance difference on sRGB values (Rec. 709 weights, no gamma), a proxy for
@@ -123,7 +128,7 @@ pub const FADE_OUT_FRAMES : i32 = 8;
 pub const STILL_CARD_ALPHA : i32 = 1000;
 
 /// The palette, 0xRRGGBB.
-pub const BACKDROP : i32 = 0x06060B;
+pub const BACKDROP : i32 = 0x000000;
 pub const AURORA_COUNT : i32 = 4;
 pub const AURORA : [4]i32 = [0x7C3AED, 0xC026D3, 0xF472B6, 0x3B82F6];
 pub const TEXT : i32 = 0xFFFFFF;
@@ -135,9 +140,9 @@ pub const GLASS_FILL_PERMILLE : i32 = 70;
 pub const GLASS_BORDER_PERMILLE : i32 = 240;
 pub const GLASS_RADIUS_PERMILLE : i32 = 32;
 /// How much of the aurora shows through behind a card, and behind the cover headline; how strongly
-/// the map shows behind the cover.
-pub const AURORA_UNDER_CARD_PERMILLE : i32 = 300;
-pub const AURORA_UNDER_COVER_PERMILLE : i32 = 450;
+/// the map shows behind the cover. The brand backdrop is black, so no aurora shows anywhere.
+pub const AURORA_UNDER_CARD_PERMILLE : i32 = 0;
+pub const AURORA_UNDER_COVER_PERMILLE : i32 = 0;
 pub const COVER_MAP_PERMILLE : i32 = 250;
 
 /// Cell colours on the dark slide, indexed by reel.t27 STYLE_*: gap, muted, open, draft, verified,
@@ -632,6 +637,19 @@ test decoration_never_wears_a_status_colour {
     }
 }
 
+test the_backdrop_is_brand_black {
+    assert BACKDROP == 0x000000;
+    var i : i32 = 0;
+    while (i < AURORA_COUNT) {
+        // a ribbon at card strength and at cover strength leaves the backdrop black
+        assert mix(BACKDROP, AURORA[@intCast(i)], AURORA_UNDER_CARD_PERMILLE) == 0x000000;
+        assert mix(BACKDROP, AURORA[@intCast(i)], AURORA_UNDER_COVER_PERMILLE) == 0x000000;
+        i = i + 1;
+    }
+    // the darkest status colour (muted) still stands off pure black
+    assert distance(style_colour(STYLE_MUTED), 0x000000) >= MIN_STATUS_DISTANCE;
+}
+
 test gaps_stay_loud_on_a_dark_slide {
     assert style_dashed(STYLE_GAP);
     assert style_dashed(STYLE_UNKNOWN);