Listing talks given at home institution on CV I've given many talks at my home institution, at the undergraduate and graduate colloquiums, and in a few seminars. The list is getting quite long. 

Is it appropriate to list many talks given at my home institution? Does it reflect badly on me?
First of all, it's great that this list is becoming long!  It's good to be taking every opportunity you can as a student to practice presentations, and many students try to avoid this rather than embrace it.

Now, as for what to include in the C.V.: while in principle you can include anything, in practice you want the C.V. to convey "here are all of the things I've done that I think are significant".  Thus, it's not the question of home institution per se, but the significance of the talk venue that matters.  For example: if you were invited to give a talk in a seminar series where most of the other speakers come from other institutions, that's nearly as significant as giving a talk elsewhere.  Giving a required talk in the internal graduate colloquium matters much less.

I would recommend keeping some evidence of the fact that you are giving many presentations on your C.V.  To keep it from feeling like filler, however, you can compress the "unimportant" talks into a single bullet point, like "NN presentations in internal meetings, seminars, and colloquiums."  That conveys the information without feeling spammy.  Once you've built up a significant record of giving talks at external venues like conferences and other institutions, then you can drop that bullet point as being assumed.