Harang, who signed a one-year deal worth $4 million with the Padres in December, needed 23 pitches to complete two innings.
"I felt like everything was nice and easy," Harang said. "The ball was coming out of my hand well."
Harang was so efficient he threw 12 more pitches in a postgame bullpen session to reach his pitch count.
"I thought he was crisp," Padres manager Bud Black said. "He threw good angled fastballs and his slider was solid."
Venable, a strong candidate to be San Diego's leadoff hitter this season, also singled in three at-bats. His homer on a 1-2 fastball from Matt Reynolds made it 6-1 in the bottom of the fifth inning.
Troy Tulowitzki had two hits including a two-run homer for Colorado.
Ubaldo Jimenez, who has already pitched this spring, was scheduled to start for the Rockies but was scratched with a nail infection on his throwing hand.
"He felt instantaneous relief," Tracy said. "I don't think it was all that bad."
Jimenez, who was 19-8 with a 2.88 ERA in 33 starts last season, played catch on Wednesday and will play long toss again on Thursday.
If he stays healthy, Jimenez could throw a bullpen session on Friday. Jimenez had the first no-hitter in Rockies history on April 17 and finished third in voting for the NL Cy Young award.