Yes
It depends on the amount of residue.
No, It's possession of a narcotic paraphernalia
If there is a sufficient measurable quantity of the residue and it meets the minimum for placing charges, yes, you could be charged with 'possession."
See: http://www.greenwoodvillage.com/municode/_data/title09/Chapter_9_12__OFFENSES_AGAINST_PUB/9_12_140_Illegal_possession_of.html