Comment by 0tfoaij

Obliged to point out that Latin -or words were often spelled with -or, -our, and -ur in Old French also. If you are using Wiktionary as a source you have to click through to the Old French definitions to see the alternate forms, as well as parsing the descendant table to see the derived forms that the simple etymology blurb often leaves out. Doing so you can also see that Middle Dutch has 'coleur' (modern kleur) which very likely did not originate from Middle French given the timeframe.

The earliest quotations for colour in the Oxford English Dictionary are from around 1300 where it was spelled 'colur' (cf Welsh) which while being post-Norman England is not post-Norman English. For Norman/Angevin-England the OED also has a quotation for honour as 'onur' listed as before 1200 (and again as 'onour' from around 1300). If you want to make a case of superfluous 'u's being added a better example would be something like chancellor, where the 'u' was added in Middle English and then later removed, rather than colour (or honour) where the 'u's have existed since the earliest quotations. The reason color and honor stuck about in English is most likely because that is how they were spelled in Latin.