I'm sorry to hear of your loss.
Your question raises a question in my mind: Why do you feel you will need to contest this will? If your mother lived in Colorado when she died, that is where the will should be probated, but that doesn't mean it can't be read now and in a location that is more convenient for everyone.
If you don't know what is in the will or who is the executor/personal representative, you *should* open it and read it before filing probate as that will define who should do what. I STRONGLY urge you not to do that alone however, but get together with your siblings, and do it together lest there be suspicions.
If you are uncertain on how to do this, you should consult with a Colorado attorney to have some help walking through the process.