Alcohol stove fuel question

Not a biggie, just something I was wondering about. I noticed on minibull's Youtube videos that his fuel is blue or green. Is that just food coloring to help detect leaks or spills? Or is he using something that comes colored. My denatured alcohol is clear, and if Heet has a slight color, I don't remember it being vivid blue/green like that.

That's food coloring. So no one will mistake the fuel for water.

ah - didn't think of that angle...