Colorado Gun Laws

Under the 15-round limit law, smaller magazines with removal base plates are also outlawed — a measure that affects most handguns and many rifles, Kopel said of the move to limit gun ownership.

I've seen different interpretations of this ranging from "pay no attention to it"  to yes, any magazine with a removable floor plate is effectively banned.

I suppose it will be like most laws passed here, interpretation will be left to the cops judgement and/or orders from higher ups.

The city and County of Denver has always taken the most draconian interpretation of all legislation, and if it can't be over-interpreted, they write their own municipal statutes to fill in any perceived gaps. If you want a semiauto pistol, you'll have to buy it outside of Denver if you want any magazines at all to go with it.

Either that, or this law, like most of the others, will be widely ignored. 

There is a lawsuit started to overturn this, but getting anything through the courts typically takes a long time.