How can a person determine wheter a Colt lower is a large pin vs a small pin lower?  Preferably by sight without complex testing(hehe).

That's actually a good question, Biggun.  Most of us here (especially myself, since that's what I own) go by the standard that any post-ban Colt (Match Target, MT HBAR, MT Competition, etc) uses non-standard, i.e. LARGE pins.

To tell by the eye is very hard, unless you visibly put your Colt next to, say, a Bushmaster - and see that the Colt's trigger
pins are [i]slightly[/i] bigger.  As far as takedown pins go, I believe that Colt has now gone back to the standard sized front and rear pins (I believe it used to be that one was smaller than the other, and needed some kind of bushing to attach to a mil-spec upper - somebody correct me if I'm wrong please).

If you have a new Colt, and you're worried about attaching a different upper receiver to it, then it shouldn't be a problem.  The big fuss recently has been that some aftermarket 2-stage triggers and such don't fit well with the non-standard pins, and need gunsmithing to work (instead of the typical do-it-yourself).  This is the basic idea, somebody else will probably give you a timeline of what was changed (due to Colt wanting to make Washington happy) and when.

But this is a start.
Jewbroni~

I was looking at a pre ban Colt and I got to wondering if my extra parts such as pins triggers etc would work or not.  If the prebans are supposed to have small pins that is what it probably has.  Thanks guys