use okchla color for better movement between shades

src/bin/flappy/main.rs

@@ -1275,14 +1275,11 @@ fn debug_trail(
 
 fn shimmer_button<T: Component>(mut bg: Single<&mut BackgroundColor, With<T>>, time: Res<Time>) {
     let t = time.elapsed_secs();
-    let period = 3.0;
-    let red = (((t / period) % 1.0) * std::f32::consts::PI).cos();
-    let green = ((((t / period) + 0.3) % 1.0) * std::f32::consts::PI).cos();
-    let blue = ((((t / period) + 0.6) % 1.0) * std::f32::consts::PI).cos();
-    bg.0 = Srgba {
-        red,
-        green,
-        blue,
+    let lightness = 0.5;
+    let chroma = 0.5;
+    let hue = (t * 60.0) % 360.0;
+    bg.0 = Oklcha {
+        lightness, chroma, hue,
         alpha: bg.0.alpha(),
     }
     .into();