You are probably OK with a straight cat5e Ethernet cable, colour irrelevant in this case.
Personally I'd get one off ebay
http://cgi.ebay.co.uk/10-Meter-CAT5e-RJ45-Ethernet-Network-LAN-Cable-Lead-10M_W0QQitemZ360200912287QQcmdZViewItemQQptZUK_Computing_CablesConnectors_RL?hash=item53dda5bd9fbut if you are in a hurray you can get one made up in Maplin for several times that price.
Lastly are you sure its the wireless that is the issue? Personally my PS3 had been unplayable online for a while, turns out Netgear screwed the firmware in my router - I rolled back a version and its OK again!
Not saying it isn't a wireless issue, but it could be something else (but £2 for a cable to find out isn't too much of a risk!).