Add support for rendering tinted artwork.

OpenRA.Game/Primitives/float3.cs

@@ -62,5 +62,6 @@ namespace OpenRA
 		public override string ToString() { return "{0},{1},{2}".F(X, Y, Z); }
 
 		public static readonly float3 Zero = new float3(0, 0, 0);
+		public static readonly float3 Ones = new float3(1, 1, 1);
 	}
 }