Author the player X-ray glow color and fade timing

Set _XRayColor (HDR orange, alpha 0 = off by default), pulse speed/strength
on Player.mat and xrayFadeDuration on the Player prefab.

Assets/Prefabs/Player.prefab

@@ -480,6 +480,7 @@ MonoBehaviour:
   sprayDotAlphaMin: 0.25
   sprayDotAlphaMax: 1
   maxUndoSteps: 20
+  xrayFadeDuration: 0.15
   useGpu: 1
   paintAlbedo: 1
   paintMetallicSmoothness: 0