Under Colorado's expressed consent law, you have the right to demand a blood test if you are suspected of driving drunk. You absolutely have the right to refuse to provide a sample of your breath or blood.
In certain limited situations, the police may obtain a sample of your blood without your consent and may even physically restrain you for these purposes:
If you are a suspect in a criminally negligent homicide, vehicular homicide, assault in the third degree or vehicular assault.
If the officer obtains a search warrant by articulating probable cause to a judge. This is treated exactly like a search warrant for a home, except that now the enclosed space to be searched is your body.