Old new tyres

[Chillout47]

I have a restored losi XXX that is let down by its tyres. They have started to go brown in some areas (they are unused), I presume this is something to do with the natural rubber content. Anybody got a good way of cleaning old tyres up? I would like to get them nice and black and shiny to match the rest of the car so I presume I will need some kind of coating?

Cheers chaps - Mark.