The American English, and the British English are very different, and complex, Even though they are both the same lanuage.
The English Lanuage has many spellings for each word through out the world. Your best bet is to stay with British Spellings, People can still read the words the same.
Spellings that are different.
Colour - Color
Centre - Center
Aeroplane - Airplane
I could go on and on and on... but here is a link, telling you many different spelling differences, but trust me, there are many more.
http://en.wikipedia.org/wiki/American_a ... ifferences