Painting a floor mat requires a paint that is flexible enough to give with their bendable material, strong enough to resist chipping, cracking and peeling when dirt and stones are ground into it with the heels of your shoes, and vibrant enough to cover the dark colors that floor mats come in. The paint actually needs to bite into the rubber to form an impregnating tightly locked bond. Craft and commercial paints won't give you the paint you need to do the job right; but you can make a rubber paint to use to paint a floor mat.
Wash the car mat with a sponge dipped in a mild detergent and water solution.
Rinse it with direct spray from a garden hose and place in in the sun to dry.
Put on gloves and face mask to protect yourself from the toxic rubber cement fumes.
Mix 15 oz of rubber cement and 3 oz of oil paint in a canning jar, and add enough mineral spirits to make the rubber paint mixture a pourable consistency.
Paint the top of your floor mat with a paintbrush dipped in the rubber cement paint. A heavy coat that includes the edges of the mat is best.
Allow the paint to dry completely before painting the back or applying any additional layers or accents.
