Colour --> Color, not lazy edition

This does not rename any current vars since that is a much more >effort required problem. It simply renames the two files, colour.dm for shoes and chemistry-colours.dm. Those are the only two filenames that use the 'colour' spelling so this is proper consistency. If I find any more spellings in descriptions and names down the line I will change them, to keep with consistency that -players- see. It's bad for future contributors when the colour spelling in the code is just a workaround to the 'color' var bug from recent-ish byond versions, and those vars will still need to be renamed eventually..

Anyway, the files in clothing/under and clothing/gloves both use the 'color' spelling so shoes being colour is inconsistent. Chemistry.colours also doesn't use the word 'colour' once inside the actual file, and it's the only other file using that spelling.

Grammar nazi out.