Speaker cone fading

Does anyone know of a way to recolour the rubber edge of a speaker cone? One of my speakers received a bit too much sunlight and alas I have now noticed it has faded from black to grey and doesn't match the other.
Is the edge foam, or butyl rubber? If foam, they'll probably need new surrounds eventually, so just wait. If butyl, try wiping the surrounds with a cotton pad onto which you've sprayed (just lightly!) a little "spray silicone lubricant" (Auto Zone, Pep Boys) and that should bring the color back and condition the rubber.

If it doesn't bring the color all the way back to black, just leave it alone. My concern (if it's butyl rubber, and it has faded to gray) would be that the material has been damaged (made brittle) by the exposure to UV. If that's the case, have both woofers refitted with new surrounds.
There is a product I use for detailing my motorcycles and car that does a *spectacular* job in restoring a deep black color to vinyl, rubber, painted metal, etc. It has never damaged anything I've used it on. It is called S-100 Engine Brightener and costs about $8.00 a can. Look for it at motorcycle shops or online...