Well I hadn't heard this one. The Latin words for 'colour' and 'honour' are color and honor. I suppose it's conceivable that he adopted some arbitrary rule such as
"Latin -or → English '-our'; Greek -ωρ → '-or'but I can't think of a Greek example (ύδωρ gives us lots of 'hyd-' words but not - as far as I know - *"hydor").
What I do know is that when Johnson jokingly defined 'lexicographer' as 'a harmless drudge' he was seriously (disingenuously?) underestimating the harm that a lexicographer can do; and that Noah Webster's keeping the endings for 'color' and 'honor' was etymologically justified.
PS I'm as British as the next man (as long as the next man is British ), but I rate Webster way above Johnson in the 'services to English' stakes, important though Johnson was in many fields.
Student or Learner