Flexible Paint is a coating for surfaces that bend. It stays pliable after drying, so on rubber tracks, latex accessories or flexible mats it does not craze and lift the way ordinary acrylic does after a few flexes. The 240 ml bottle assumes you are covering areas rather than picking out detail, which is exactly the kind of job it exists for.
Degrease the surface first, because rubber and latex usually leave the factory with a film on them and no coating will grip, flexible or not. Work with a brush or a wide flat tool and let the layer dry without stretching the material. If a metal shade is going over the flexible base, the metallic range carries metals in the same flexible formulation. The maker's other lines, inks and effect paints included, are in Green Stuff World acrylic paints.