Leading 3-0 going into the eighth, the Rockies sent 10 men to the plate, banging out six hits en route to seven runs, turning the contest into a rout.
Colvin also socked a solo homer in the first inning while DJ LeMahieu added a pair of RBI singles for the Rockies, who took the first of a three-game series.
Jeff Francis (5-4) tossed five shutout frames to earn the win, scattering three hits. He walked one and struck out six.
Josh Roenicke and Rex Brothers combined for 2 1/3 scoreless innings and Matt Belisle recorded the final five outs for his second save.
Los Angeles starter Josh Beckett (0-1), acquired from the Boston Red Sox Saturday as part of a blockbuster trade, was touched for three runs on seven hits over 5 2/3 innings in his first appearance as a Dodger.
Second-place LA fell 2 1/2 games behind idle San Francisco in the race for the National League West title with the loss.