Cummings, who has scored six times in 21 appearances for his national team, arrives on the back of helping the Rapids to their first-ever MLS Cup triumph.
He scored a career-high 14 goals in the 2010 season, as Colorado qualified for the play-offs, before going on to be crowned overall MLS champions.
Cummings has developed into one of the most feared strikers in the US league, earning numerous Player of the Week and Goal of the Week awards since being drafted in 2007.
"Somebody mentioned him, we enquired, we looked at some videos and said we would have him here on trial," Houllier told Villa's website.
"He's a bit jet-lagged because he only arrived on Wednesday. I don't think we can say yet when he will be involved.
"We need a work permit and many things so we will see. He's got a nice personality. There's no cost and no risk.
"He is quick and can also play on the wing. Don't forget we have not many options up front at this time."