use Color4 constants

Program.cs

@@ -307,7 +307,7 @@ public class Game : GameWindow {
       Rectangle box = new Rectangle(windowWidth - thumbnailWidth, i * thumbnailHeight, thumbnailWidth, thumbnailHeight);
       DrawTexture(textures[i], box);
       if (i == textureIndex) {
-        DrawBox(box, 3, new Color4(1f, 1f, 0f, 1f));
+        DrawBox(box, 3, Color4.GreenYellow);
       }
     }
 
@@ -315,7 +315,7 @@ public class Game : GameWindow {
   }
 
   void DrawTexture(Texture texture, Rectangle box) {
-    DrawTexture(texture, box, new Color4(1f, 1f, 1f, 1f));
+    DrawTexture(texture, box, Color4.White);
   }
 
   void DrawTexture(Texture texture, Rectangle box, Color4 color) {