So read through the bill again. No you do not have to be a resident of Colorado. You must simply possess the magazine prior to the effective date of the ban.
An interesting point I didn't know before;
Any magazine manufactured in Colorado after the effective date of this bill must have an identifying mark stamped or engraved upon it to indicate it was manufactured after the effective date of the ban.
This part is what gets me;
(I) A FIXED OR DETACHABLE MAGAZINE, BOX, DRUM, FEED STRIP, OR
SIMILAR DEVICE CAPABLE OF ACCEPTING, OR THAT IS DESIGNED TO BE
READILY CONVERTED TO ACCEPT, MORE THAN FIFTEEN ROUNDS OF
AMMUNITION;
So basically any magazine with a removable base plate could be considered readily convertible to accept more than 15 rounds. What a yoke.