perf: editing theme doesn't require a complete reredenring

tests/shader_valid.rs

@@ -25,6 +25,11 @@ fn mandelbrot_shader_is_valid() {
     );
 }
 
+#[test]
+fn colorize_shader_is_valid() {
+    validate("colorize.wgsl", include_str!("../src/shaders/colorize.wgsl"));
+}
+
 #[test]
 fn blit_shader_is_valid() {
     validate("blit.wgsl", include_str!("../src/shaders/blit.wgsl"));