I flew this route numerous times in the 87-90 era. As stated, it began with a DC9-10 series and did allow those of us trying to get to Galveston a head start from IAH. The plane kept deteriorating over the years until it was the last 10 series in service with CO and you could tell that they were doing nothing to the interior since it was falling apart. And you are right, I remember it being run as "Emerald Air". Since I was on the last flight of the evening, these were usually empty flights but I think that was because CO made you wait 2 hours between arriving at IAH and catching the connection. Eventually they discarded the DC9 but I do not remember them using B-1900s. They then dumped HOU and moved to EDF, with the ATR 42s (a miserable plane).

What was really great in those years was that CO also serviced AKR to CLE with EBR-130s (Brazilia's) which meant that I could get 3 segments and an extra 1000 miles on each flight to Houston and actually have more convenient service. I think that 9/11 washed all of that away.