The origins and development of a language can be quite fascinating.
The -or vs. -our endings reflect the many influences over English. In a word like color/colour, the -or version more accurately follows the original Latin - coloris - whereas the -our ending was influenced by the French couleur. Apparently both forms were actually used in England in the past, but gradually colour became the generally accepted spelling. There are anomolies though, and to this day British dictionaries list colour, coloured, colouring, but.... coloration. There is a similar inconsistency with some derivatives of humour and honour in which the u is dropped. Webster's preference for the -or spelling in all cases is far more logical.
There are other spellings which are also more consistent in the "American" version, e.g. British defence, defensive vs. American defense, defensive.
On -ize vs. -ise, I find it curious that so many people in Britain (and Ireland, NZ?) regard spellings such as realize and recognize as being "Those ignorant Americans corrupting the language again." In fact, it would be far more accurate to say that the -ise ending is a British corruption, and a comparatively recent one at that. My King's English dictionary from the 1930s lists the -ize forms as standard, with a note that -ise is an acceptable alternative. I've seen an 1890s dictionary which doesn't list the -ise forms at all. And although the -ise spellings might be the most common in more modern times, some of the heavy-duty technical publishers (e.g. Pitman) certainly still used -ize as their house style up until at least the late 1960s.
