I did a recent article on non-slip shelf liners, and noted that only certain colors are available at certain retailers. For example, Dollar Tree doesn't carry green shelf liners. Rite Aid drug stores stock green shelf liners in their Dollar Deals aisle, but those stores are closing due to bankruptcy.
So the question arises: can you paint non-slip shelf liner to get your preferred terrain color?

Above, you can see a scrap of white shelf liner left over from a previous project.

I taped the scrap piece down to my painting box, and spray-painted it with Rust-Oleum gloss green, which is a paint-plus-primer that claims to 'bond to plastic'.

To my great surprise, this seems to work! Note that the paint on the shelf liner takes forever to dry – the overspray was dry on the painting box in hours, but the shelf liner was still tacky for four days. But as you can see, the painted shelf liner is still flexible and the paint is not flaking off (so far).
This suggests you might get away with painting non-slip shelf liner for custom terrain projects…