Purple only
Yes you can and they don't have to be purple, like Joel W Cabrera said, they have to be a certain size. And of course no metal tips
From the Rockies/MLB website: Umbrellas (During the threat of inclement weather, umbrellas are allowed at Coors Field. In consideration of the safety and sight lines of others, please use only small, compact umbrellas (28" - 34"). Large golf umbrellas and umbrellas with metal tips are strongly discouraged.)
Yes you can!
No
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