Piggies body temperature are similar to ours.
A cold nose to me may indicate something brewing - is he fluffed up at all (they do this to keep themselves warm by trapping air in their hair hence look fluffy)
Is there any change in habits, eating/drinking etc. How do his poops look ?
Lots of questions to ask yourself but the better choice is a vet visit for a check up if you are concerned.
http://www.guinealynx.info/emergency.html
http://www.caviesgalore.com/faq/medical.html
I'm always checking my piggies feet and ears to see if they are warm etc. even though they are indoors mallethead Just my paranoia rolleyes