In order to count as a "prior" DUI in California, the out-of-state conviction must have all of the same elements as a California DUI.
For instance, a DUI in California must including actual driving, which means movement of the vehicle. Other states allow DUI convictions when the person is "in control" of the vehicle, which can mean sitting in a car, drunk, with your keys in your pocket. A conviction under one of those statues cannot be used as a "prior" DUI in California.
If your Colorado conviction would not be a DUI if you did the same thing in California, you can file a petition for writ of mandate with the Superior Court in your county, asking a judge to order DMV to impose a first offense suspension. This is a complicated process and you will probably need an attorney's help. Most experienced DUI attorneys are familiar with this process.
Please understand that this is a general discussion of legal principles by a California lawyer and does not create an attorney/client relationship. It's impossible to give detailed, accurate advice based on a few sentences on a website (and you shouldn't provide too much specific information about your legal matter on a public forum like this site, anyway). You should always seek advice from an attorney licensed in your jurisdiction who can give you an informed opinion after reviewing all of the relevant information.
Although the CA DMV has taken the postion that the CO DUI was a prior, that may not be a defensible position. Filing a Writ of Mandamus to challenge the DMV's position can result in the judge finding that the prior doesn't count as a prior--but an attorney would need to review the elements of a DUI in Colorado, and compare those to the elements of a California DUI. I suggest that you check with an attorney experienced in this area of law-because it the DMV continues to insist that this is your 2nd DUI, they will suspend you for a year, require an 18-month alcohol school and the installation of an interlock device. Contrast that with the penalties if the DMV views this one as a first offense-a 3-month alcohol school, and loss of driving privileges for a maximum of 30 days. -Mindy McQueen
California's DMV will use prior convictions from anywhere in the nation as long as they are similar to what would be considered a DUI in California. If you are trying to keep a California driver's license you will probably have to enroll in and complete a portion of the SB38 18 month alcohol education program for 2nd offenders. To get into the SB38 you will either have to go to court and reopen your 6/09 case or petition the DMV to give you permission to enroll in the SB38 on your own.