I thought about using shoe polish but then it has all these petroleum chemicals so the whole thing would eventually dry out and even possibly crack so although it would work well I'd use this as a last option.
I found a better option for it though, few pics:
This is how they looked like AFTER cleaning:
After first coat:
And how they look now:
TBH, pics don't even show how good they look now, I could pick up a brand new set from JCP and I suspect I'd find it hard to recognize which one is new
So what did I use?
This little gem:
~£5, lots to pick from. Dye in this works really well with rubber, after it dried it feels permanent, doesn't stain and its not slippery at all, rubber feels like new
I'm chuffed to bits with this, can was enough to do all 4 mats
1997, 4.0 LWB X300 - Unlucky car but still a daily driver.
1988, 3.6S XJS - Never ending restoration project.
1994, 3.2S X300 - Accident damaged, October 2015. Gone!
1994, 3.2S XJ40 - Long gone.