Any issues with wearing leg warmers over tights?
I've worn my knee warmers under my tights, it worked well to keep me warm and they stayed in place well.  However, the tights were the kind that went over top of my standard bib shorts, not the kind of tights with integrated chamois.  

If you want to try and wear them over your tights, you might need to get a larger size kneee warmer, depending on the thickness of our tights. You might also have trouble with them staying put, since they tend to be held up partially by the bottom of your cycling shorts.  

Personally, If it's colder than my comfort zone with just tights, I'll usually wear a pair of stretchy synthetic knickers on warmer days (like chrome telegraph knickers) or some breathable shell pants (north face resolve) on colder days over top of my tights to help kill the wind and retain more heat.