What's the difference between AMERICAN and BRITISH spelling?

This is not a quick question to answer, but once looking at it in terms of groups of words, it is not so hard.  There are two groups of words: Latin-derived and Greek-derived.  Keep in mind the abbreviations used here:

Am.E=American English 
Br.E=British English

Latin-derived Words

Humor or Humour?

Humor is American spelling while humour is British. Here are more examples...

Am.E=humor, neighbor, behavior, color, rumor, honor, flavor
Br.E=humour, neighbour, behaviour, colour, rumour, honour, flavour

Center or Centre?

Americans use the suffix "er" while the Brits use "re".

Am.E=center, theater, luster, somber, liter, meter, fiber

Br.E=centre, theatre, lustre, sombre, litre, metre, fibre

Greek-derived Words

Realize or Realise?

Americans use the "ize" suffix while their British counterparts use the "ise" ending. 

Am.E=realize, organize, recognize, apologize, modernize, colonize
Br.E=realise, organise, recognise, aplogise, modernise, colonise

Analyze or Analyse?

Americans use the "yze" suffix while their British use the "yse" suffix, a reverse of above.

Am.E=analyze, paralyze, catalyze

Br.E=analyse, paralyse, catalyse