Washington had won four in a row and seven out of nine while moving a season-best 16 games above the .500 mark.
Colvin hit a solo shot in the second and added a two-run blast in the fourth, running his total to 13 home runs for the year.
Dexter Fowler then tacked on a solo homer in the seventh and Michael Cuddyer drove in the final Colorado run with a sacrifice fly in the eighth.
Starter Drew Pomeranz (1-3) lasted 6 1/3 innings to get the victory. It was his third win in the majors, having gone 2-1 with the Rockies last year.
Betancourt retired all three men he faced to pick up his 14th save.
Stephen Strasburg (9-4) gave up three runs, one of them unearned, on eight hits in six innings to take the loss. Strasburg has dropped his last three starts.
Texas principal bans speaking Spanish, stirs controversy
Toddler uninjured after being knocked over by Obama family dog