There are many kinds of assassin bugs in Colorado. The one I see all the time in my yard is Zelus luridus  http://webdoc.agsci.colostate.edu/bspm/Hexapoda%20(Insects)/ZelusRevised2017.pdf  Late in the season ambush bugs http://webdoc.agsci.colostate.edu/bspm/Hexapoda%20(Insects)/Ambush%20Bug.pdf are seen commonly at flowers.

One of them sometimes comes into houses or outbuildings, the masked hunter  http://webdoc.agsci.colostate.edu/bspm/Hexapoda%20(Insects)/MaskedHunterRevised2017.pdf but the rest remain outdoors.

All of them can give a good bite if handled or accidentally confined against the skin, but that is very uncommon.  They are not aggressive and will bite only in defense.

But everyone reports that the bite is quite painful.

I have never heard of a case in Colorado where someone had such a reaction to the bite that it required hospitalization, although it may well have occurred on occasion in Colorado and is reported elsewhere - particularly from the southern US where they have some species of assassin bugs that produce a more painful bite than do the Colorado species.