a) There is no difference in meaning between labor and labour. Labor is the preferred spelling in American English, and labour is preferred throughout the rest of the English-speaking world. One exception: In Australia, the American spelling is used in reference to the Australian Labor Party. In all other contexts, Australians use labour.
b) Grey (British English) or gray (American English) - Grey became the established British spelling in the 20th century, but it is a minor variant in American English, according to dictionaries. Canadians tend to prefer grey. The two spellings are of equal antiquity, and the Oxford English Dictionary states that "each of the current spellings has some analogical support". Both Grey and Gray are found in proper nouns everywhere in the English-speaking world.
@germanicus Με προλαβες Ωραιο κειμενο btw