How do I do this effect?

I want to make it so my skeleton flashes a red when he's hit no matter which animation he's in (attack, walk, stance, etc) like this:

http://www.maxgames.com/play/one-million-skeletons.html

How do I do it?

The tint effect can be used. Here's a sample with lerp adjusting the Green and Blue channels, to get Red. You can adjust LerpScale to change the timing.

http://www.blackhornettechnologies.com/Construct2Stuff/LerpTint.capx

I like LiteTween for more lerp-like options.