Coloring flexible resin

I need to print truck tires for functional models.
As I see the flexible resin is not really rubber coloured.
How - an with what - can I color it?
I have special resin pigment for casting resin? can this work?

Sadly, enamel based paints do not work well. When dry, flex leads to cracks. Water based high quality ink I used for my fountain pen worked, and it does not crack, however, I can not get it as vibrant as enamel paints. Probably I need some kind of white undercoat, but I don’t know what I can use.

Flex V2 is quite close to rubber colored especially compared to Flex V1. We used it to make some mini tires for the Flex V2 materials page. Rubber is white by default but typically has black added as a colorant. What color are you going for specifically?

What about painting it with colored latex. You can color ordinary latex using cake icing dye. The gel form, not the liquid.