I'm assuming a Democrat is appointed to finish her term.
We're talking the state Senate, not the US Senate. Colorado law may not allow the Governor to appoint replacements (I know in Texas, the Governor has to call a special election).
ETA: Colorado Constitution Article V, Section 2, states that any replacement will be of the same political party that the prior member was, if that member was affiliated with one. So a Democrat will be the replacement.
But there is a quirk: if the term was less than half-completed (i.e., less than 2 years of a 4-year term), then if the appointee wants to complete the entire term, s/he must stand for election to complete the remaining half.
This post was edited on 11/27 at 1:08 pm