Does anybody know how to properly tint an acrylic lens?  I have an extra refractor for a Nema head and I want to tint it red so I can convert it to a fire Nema.

A colored insert foil?

Art supply stores sell "stained glass paint" that can be applied to acrylic (and Lexan, I think). It is at least somewhat transparent, although it is intended to be used on the inside of windows. I don't know how it would resist to the weather. You would need quite a bit since the refractor is not a smooth surface. I have never tried it myself but it might be an option to consider.

Topic is nearly a month old but I'd try this... Go to your favourite dollar store; they have very cheap art supplies (fine brushes, small canvas frames & various tubes of paint). Get a red tint water-based artist paint. Dilute it with water, and brush the INSIDE of your acrylic lens. Let it dry. Then wash it. Not all of the paint will wash away as the lens absorbs the paint somehow. Repeat as many times you can afford.