Paint.

There is vinyl paint for that job from local motor vehicle paint factors

 

The brands tend not to be too important unless your colour matching top end pearls on premium supercars

 

I am thinking about doing the same on my Bonnie, and I found that sneaker paint, it's apparently good for leather and vinyl :

http://www.adam-eshop.com/en/paint-for-custom-sneakers/1627-angelus-leather-paint-gold.html

They also sell a transparent varnish to protect it and a "duller" to make it look less glossy. Anyone tried that ?