diff --git a/projects/kissaten_yugure/docs/ART.md b/projects/kissaten_yugure/docs/ART.md
index 7d92560..dbc6187 100644
--- a/projects/kissaten_yugure/docs/ART.md
+++ b/projects/kissaten_yugure/docs/ART.md
@@ -86,13 +86,28 @@ Character notes in `SCRIPT.md` §1. Written as a girl there; that's one word to
 change if you'd rather — the dialogue beats themselves use no gendered
 pronouns.
 
-**Common style stem** — prepend to all three:
+### Portrait palette block — paste into every portrait prompt
+
+Portraits never show sky, so the four sky slots are simply absent from the
+list. That is safer than asking the generator to avoid them.
+
+```
+Use only these 11 colours and no others:
+#242424 #492424 #924924 #B66D49 #FFB649 #FFDB92 #6D4949 #6D2400
+#496DB6 #FFB692 #FFFFDB
+Skin: #FFDB92 highlight, #FFB692 base, #B66D49 shadow, #924924 deep shadow.
+Hair and outlines: #242424 or #492424.
+Eye whites and highlights: #FFFFDB.
+Fill the entire background behind the head with flat #492424.
+Do not use pure black #000000 anywhere.
+```
+
+**Common style stem** — prepend to all three, then append the palette block:
 
 > 48x48 pixel art portrait, 1987 Japanese anime style as drawn for MSX2 or
 > PC-88 games, head and shoulders, three-quarter view, hard-edged pixels, no
-> anti-aliasing, limited 16 colour palette of warm browns oranges and creams,
-> flat cel shading, dark navy school uniform, simple readable silhouette,
-> plain dark background
+> anti-aliasing, flat cel shading, simple readable silhouette, flat single
+> colour background
 
 **Aki — neutral**
 > ...17 year old Japanese high school student, straight dark bob-length hair,
@@ -112,7 +127,11 @@ pronouns.
 
 ## 4. Prompts — the rest of the cast (M8, not urgent)
 
-Same style stem, swapping the uniform line.
+Same style stem and the **same portrait palette block from §3**, swapping the
+clothing line. Note the clothing colours available are only `#496DB6` (blue),
+`#6D4949` (muted brown-grey), `#6D2400` (dark red-brown), `#492424` and
+`#242424` — so give each character a distinct one or they'll blur together in
+the dialogue box.
 
 **Ōta-san** — retired stationmaster, ~70, black coffee, punctual.
 > elderly Japanese man in his seventies, close-cropped grey hair, deeply
@@ -158,10 +177,38 @@ Composition is fixed by the code — see `DESIGN.md` §4 and `DrawScene()`:
 > violet and amber dusk sky, wooden door on the right, hanging lamp with warm
 > glow above the counter, wood panelling, shelves with glassware, cosy and
 > quiet, 1987 MSX2 game art, hard-edged pixels, no anti-aliasing, flat cel
-> shading, warm brown and orange interior with the sky in violet and amber
+> shading
 
-**The sky through that window must use only slots 8–11.** Everything else in
-the room must avoid them. That's the whole seasonal system riding on one rule.
+### Background palette block — this one is split by region
+
+Unlike the portraits, the background needs all 15 colours — but **which
+colours may appear is decided by where you are in the image**. This is the
+constraint that makes seasons free, and it is the easiest one to get wrong.
+
+```
+Use only these 15 colours and no others.
+
+For the sky visible through the window, use ONLY these four:
+#492492 #9249B6 #DB6D6D #FF9249
+
+For everything else — walls, floor, counter, door, window frame, lamp,
+shelves, glassware, every object in the room — use ONLY these eleven:
+#242424 #492424 #924924 #B66D49 #FFB649 #FFDB92 #6D4949 #6D2400
+#496DB6 #FFB692 #FFFFDB
+
+The four sky colours must appear nowhere except inside the window opening.
+The window frame, mullions and sill are wood and use the interior colours.
+Do not use pure black #000000 anywhere.
+Leave the top 16 rows and the bottom 64 rows flat #242424 — the game draws
+its own status bar and dialogue box over them.
+```
+
+**Why this one rule matters more than the rest of this document:** each season
+and hour of day is a 32-byte palette swap on the same bitmap. Repaint slots
+8–11 and the sky goes from dusk to noon to rain for free. But if a chair leg
+or a coffee cup is painted in `#9249B6`, that chair leg changes colour every
+time the sun moves — and you won't find out until M7, long after the art is
+finished.
 
 ---
 
@@ -172,5 +219,11 @@ is the same silhouette dilated by one pixel, drawn behind. Sprite mode 2, so
 each layer is a single colour — these are shapes, not shaded art. Current
 placeholders are in `kissaten.c` as `g_SprCustFill` / `g_SprCustLine`.
 
+**Palette does not apply here in the usual sense.** These are hardware
+sprites, not bitmap art: each layer is one flat colour chosen at runtime by
+the code, so the image only needs to define *shape*. Draw them as pure
+black-on-white silhouettes and I'll assign colours — currently `#496DB6` for
+the fill layer and `#242424` for the outline, per customer.
+
 Worth doing by hand rather than generating; a 16×16 single-colour silhouette
 is faster to draw than to prompt for.