diff --git a/src/snes/ppu/bus.rs b/src/snes/ppu/bus.rs
index 99b2668..f0a7dca 100644
--- a/src/snes/ppu/bus.rs
+++ b/src/snes/ppu/bus.rs
@@ -255,7 +255,18 @@ where
                 // CGADSUB - Color Math Control Register B (W)
                 0x2131 => Some(self.cgadsub = val),
                 // COLDATA - Color Math Sub Screen Backdrop Color (W)
-                0x2132 => Some(self.coldata = val),
+                0x2132 => {
+                    if val & (1 << 5) != 0 {
+                        self.coldata = self.coldata.with_r(val & 0x1F);
+                    }
+                    if val & (1 << 6) != 0 {
+                        self.coldata = self.coldata.with_g(val & 0x1F);
+                    }
+                    if val & (1 << 7) != 0 {
+                        self.coldata = self.coldata.with_b(val & 0x1F);
+                    }
+                    Some(())
+                }
                 // RDCGRAM - Palette CGRAM Data Read
                 0x213B => None,
 
diff --git a/src/snes/ppu/mod.rs b/src/snes/ppu/mod.rs
index dfc6710..1b2e84a 100644
--- a/src/snes/ppu/mod.rs
+++ b/src/snes/ppu/mod.rs
@@ -16,6 +16,7 @@ use num_traits::{FromPrimitive, ToPrimitive};
 use crate::frontend::Renderer;
 use crate::tickable::{Tickable, Ticks};
 
+use color::SnesColor;
 use tile::{Tile, TILE_HEIGHT, TILE_WIDTH};
 
 pub const SCREEN_WIDTH: usize = 8 * 32;
@@ -148,7 +149,7 @@ pub struct PPU<TRenderer: Renderer> {
     // Color math settings
     cgwsel: u8,
     cgadsub: u8,
-    coldata: u8,
+    coldata: SnesColor,
 }
 
 pub struct BgTile<'a> {
@@ -236,7 +237,7 @@ where
 
             cgwsel: 0,
             cgadsub: 0,
-            coldata: 0,
+            coldata: SnesColor::BLACK,
         }
     }