I've reverted your edit to Blood. Wikipedia does not prefer UK over US spellings (or vice versa) and it is not helpful to 'correct' the one to the other, unless done for reasons of consistency within a page or when the topic itself indicates a particular dialect. Elizabeth II of the United Kingdom is an example of a page where it would be appropriate to impose UK spellings; Blood is not.
In particular, please don't make changes that make the page's spelling less consistent, e.g. by leaving both spellings of color/colour in the article. --Calair 01:26, 19 June 2006 (UTC)