If only to satisfy my quest for semantic purity, I submit the following. The Hummer H3 is not based on the Colorado platform. The H3 and the Colorado are both based on the Trailblazer/Envoy platform. They are, in ways, different branches of the same tree. Though the H3 has more in common with the original platform than does the Colorado. The Hummer also offers the 6 cylinder motor, which the Colorado, does not.
FWIW