I have successfully create a new Fluid and registered its Block

I am wondering if there is a way to get the Fluid to render purple when you swim in it

As of right now, it just renders the same as lava.

Do I have to use ASM or is there a better way

Using Forge 1.10.2 12.18.1.2044

I have searched Google and this forum, but I couldn't find anything

Well there is a Class called BlockFluidRenderer, I assume that might be worthwhile to look at.

Actually now that I fully understand your question, you wanted the screen color to change when the players face is in your liquid.... you want to subscribe to this event

EntityViewRenderEvent.FogColors

Thank you, I will try this later and update if it doesn't work

I use this code and registered the Event but the fog is always white!

public class SwimFog 
{
@SubscribeEvent
public void playerSwim(FogColors e)
{
	Entity ent = e.getEntity();
	World w = ent.getEntityWorld();
	BlockPos pos = ent.getPosition();
	IBlockState bs = w.getBlockState(pos);
	Block b = bs.getBlock();
	if(b.equals(GFluids.amethyst.getBlock()))
	{
		int red = 80, green = 13, blue = 147;
		e.setRed(red); e.setGreen(green); e.setBlue(blue);
	}
}

@SubscribeEvent
public void playerSwim(FogDensity e)
{
	e.setCanceled(true);
	Entity ent = e.getEntity();
	World w = ent.getEntityWorld();
	BlockPos pos = ent.getPosition();
	IBlockState bs = w.getBlockState(pos);
	Block b = bs.getBlock();
	if(b.equals(GFluids.amethyst.getBlock()))
	{
		float alpha = 234.0F; e.setDensity(alpha/100.0F);
	}
}
}

Where did you register it?