Add constants for color shades

Author: Rangi42

HISTORY.md

@@ -104,5 +104,6 @@
   - Added `PAD_*` constants for combined button and Control Pad masks
   - Added `B_COLOR_*` red/green/blue bit numbers
   - Corrected comments on `B_BG_PRIO` and `B_OAM_PRIO`
-- **Rev 6.0.0** - 2025-06-30 *(Rangi42)*
+- **Rev 6.0.0** - 2025-07-03 *(Rangi42)*
   - Changed `_AUD3WAVERAM` to `AUD3WAVERAM`
+  - Added `SHADE_*` constants for grayscale shades

hardware.inc

@@ -941,6 +941,12 @@ def COLOR_SIZE equ 2 ; size of color in bytes (little-endian BGR555)
 def PAL_COLORS equ 4 ; colors per palette
 def PAL_SIZE   equ COLOR_SIZE * PAL_COLORS ; size of palette in bytes
 
+; (DMG only) grayscale shade indexes for BGP, OBP0, and OBP1
+def SHADE_WHITE equ %00
+def SHADE_LIGHT equ %01
+def SHADE_DARK  equ %10
+def SHADE_BLACK equ %11
+
 ; Tilemaps the BG or Window can read from (controlled by LCDC)
 def TILEMAP0 equ $9800 ; $9800-$9BFF
 def TILEMAP1 equ $9C00 ; $9C00-$9FFF