The Creeper Temper mod. Creepers turn red as they start igniting.

CreeperTemper.java

package vazkii.creepertemper;

import net.minecraft.client.renderer.entity.RenderCreeper;
import net.minecraft.entity.monster.EntityCreeper;
import net.minecraft.util.ResourceLocation;

import org.lwjgl.opengl.GL11;

import cpw.mods.fml.client.registry.RenderingRegistry;
import cpw.mods.fml.common.Mod;
import cpw.mods.fml.common.Mod.EventHandler;
import cpw.mods.fml.common.event.FMLPostInitializationEvent;

@Mod(modid = "CreeperTemper", name = "Creeper Temper", version = "1.0")
public class CreeperTemper extends RenderCreeper {
  	
	@EventHandler
	public void registry(FMLPostInitializationEvent event) {
		RenderingRegistry.registerEntityRenderingHandler(EntityCreeper.class, this);
	}
	
	@Override
	protected ResourceLocation func_110829_a(EntityCreeper par1EntityCreeper) {
		if(par1EntityCreeper.getCreeperState() == 1) {
			float antired = 1F - (par1EntityCreeper.getCreeperFlashIntensity(0F) / 1.17F + 0.1F);
			GL11.glColor3f(1F, antired, antired);
		}
		
		return super.func_110829_a(par1EntityCreeper);
	}
	
}