はじめまして!
I know this is sudden for a stranger to join the group but i just need some help with kanji... see if the flow of these sentences r ok with what i wish to convey on a christmas card to a friend who lives in the States and who knows Japanese more than me :X I had some help from my cousin who's more fluent than me but i thought i'd consult others too...
Basically I'm trying to write the following in super casual form:
Didn't know what else would match the colour blue, so I thought grey would be nice. It matches with plenty of other colors so I thought, Kay just get this. Hope it''ll warm you up as you brave the cold weather wherever you go.
Lots of Love,
Donald

The link to the rough translation which heads over to IMGUR, and is written by my cousin is provided as below:
http://i.imgur.com/eZGkA4m.jpg?1

もうしわけありませんでした

Your image doesn't say what your English says although it's similar. Most notably, it doesn't say 'Hope it'll warm you up...', it says 'It's going to be getting cold, but don't catch a cold!' (although cold isn't the same word in Japanese of course).
It's okay though, conveys roughly the same sentiments. I'd rewrite it though, it's kind of sloppy and has correction marks and stuff.