reddening of skin in Unity or Renpy
 

looking to create an effect of skin reddening in either unity or renpy, any ideas? I don't want it to just pop in but rather to increase over time. Headmasters study has done it in renpy and would like to know the technique, but my prefered engine for this idea is unity.

In unity you can place a 2D sprite with 0 alpha, then increase it on event. If you have an animation you can use an animation event that increase the alpha value when the hand smacks

ahh ha frickin alpha channel. I hardly ever use it in my other stuff so I forgot about it here. Thank you kind reader.