I would always get a check (Commonly called HPI) and you can do this using a number of Companies like mytextcheck etc, although I would expect the dealer to give you the one they did when they brought the bike (Trade cost is about £3 do one) The check will let you know if there is a problem with a number of categories relating to the bike like a MAJOR accident recorded or outstanding finance, stolen etc. If you have brought from a decent dealer this should be clear for most categories however, if there is a MAJOR accident recorded then the value of the bike will be reduced. I have put the word MAJOR is caps as any small claim or where the repair has been done outside of an insurance claim may not be recorded. This, to me, is the most common reason why people randomly change the bike colour.
The bottom line is, if you are happy with the bike, and it's looks, then there is not a problem, just enjoy and remember next time you are buying.