diff --git a/projects/core/src/main/resources/data/computercraft/lua/rom/apis/colors.lua b/projects/core/src/main/resources/data/computercraft/lua/rom/apis/colors.lua
index b98ff8d75..f013a29e1 100644
--- a/projects/core/src/main/resources/data/computercraft/lua/rom/apis/colors.lua
+++ b/projects/core/src/main/resources/data/computercraft/lua/rom/apis/colors.lua
@@ -371,7 +371,7 @@ function toBlit(color)
     local hex = color_hex_lookup[color]
     if hex then return hex end
 
-    if color < 0 or color > 0xffff then error("Colour out of range", 2) end
+    if color < 1 or color > 0xffff then error("Colour out of range", 2) end
     return string.format("%x", math.floor(math.log(color, 2)))
 end
 
diff --git a/projects/core/src/main/resources/data/computercraft/lua/rom/apis/window.lua b/projects/core/src/main/resources/data/computercraft/lua/rom/apis/window.lua
index 7be7aebaf..5b5678d63 100644
--- a/projects/core/src/main/resources/data/computercraft/lua/rom/apis/window.lua
+++ b/projects/core/src/main/resources/data/computercraft/lua/rom/apis/window.lua
@@ -65,7 +65,7 @@ local function parse_color(color)
         return expect(1, color, "number")
     end
 
-    if color < 0 or color > 0xffff then error("Colour out of range", 3) end
+    if color < 1 or color > 0xffff then error("Colour out of range", 3) end
     return 2 ^ math.floor(math.log(color, 2))
 end
 
diff --git a/projects/core/src/test/resources/test-rom/spec/apis/colors_spec.lua b/projects/core/src/test/resources/test-rom/spec/apis/colors_spec.lua
index 46c77dcf8..8f50b0d56 100644
--- a/projects/core/src/test/resources/test-rom/spec/apis/colors_spec.lua
+++ b/projects/core/src/test/resources/test-rom/spec/apis/colors_spec.lua
@@ -94,6 +94,7 @@ describe("The colors library", function()
         end)
 
         it("errors on out-of-range colours", function()
+            expect.error(colors.toBlit, 0):eq("Colour out of range")
             expect.error(colors.toBlit, -120):eq("Colour out of range")
             expect.error(colors.toBlit, 0x10000):eq("Colour out of range")
         end)
diff --git a/projects/core/src/test/resources/test-rom/spec/apis/window_spec.lua b/projects/core/src/test/resources/test-rom/spec/apis/window_spec.lua
index 89e4e2993..4ad3d797c 100644
--- a/projects/core/src/test/resources/test-rom/spec/apis/window_spec.lua
+++ b/projects/core/src/test/resources/test-rom/spec/apis/window_spec.lua
@@ -59,6 +59,16 @@ describe("The window library", function()
 
             expect.error(w.setTextColour, nil):eq("bad argument #1 (number expected, got nil)")
             expect.error(w.setTextColour, -5):eq("Colour out of range")
+            expect.error(w.setTextColour, 0):eq("Colour out of range")
+            expect.error(w.setTextColour, 0x10000):eq("Colour out of range")
+        end)
+
+        it("accepts valid colours", function()
+            local w = mk()
+            for i = 0, 15 do
+                w.setBackgroundColour(2 ^ i)
+                expect(w.getBackgroundColour()):eq(2 ^ i)
+            end
         end)
 
         it("supports invalid combined colours", function()