changing cargo light to 3rd brake light

[Wayne penn]

I have an 86 k10 steps ide, I am going to be putting in a new head liner and I thought about changing the cargo lamp to a 3rd brake light.
I don't want to do any major body work to do this so I was looking for a red lens, with no luck. I remember in the 60's you could buy a bottle of amber paint to change clear front turn signals to amber. does anyone sell a red type dye?

Wayne