The flowers of all Lilacs are in one shade or another of pink or purple, as well as white and sometimes two toned. The difference between the two lie in the shape of the leaves and flower clusters. You can tell the difference in these two photos - the regular common Lilac has dark green, sometimes glossy leaves and bold, vibrant, in your face (and nose!) colour and fragrance, while the Preston lilac (this one likely a James McFarlane variety) has a much more delicate perfume and and very subtle colour palette. The leaves are paler green, almost fuzzy sometimes, and not quite as round as the S. vulgaris.
As far as origins go, Lilacs are native to the Balkans but quite easily naturalized throughout Europe and much of North America. Preston Lilacs were hybridized right here in Canada, at the Central Experimental Farm in Ottawa in the 1920's. They're more cold resistant and mildew resistant than other varieties, I find, and mine have never had a 'bad' flowering year compared to some years where I get very few blooms on the S. vulgaris.
The won't grow just anywhere - full sun is best (otherwise they'll get leggy and won't bloom as much) and they do like moist soil but not wet. I made the mistake early on of planting a bunch of them all around the back end - where the limestone was particularly close to the surface, creating drainage problems in the spring and letting the thin layer of soil get powder dry in July and August. Only three of an original eight bushes survive, and none of them are terrible happy. The Preston Lilacs, on the other hand, one of them in particular, seemed to have been able to adapt, sending down roots far enough to survive the summer, and I also happened to plant them a little higher instead of level with the normal soil surface.
I don't think I could ever get enough Lilac and plan to plant many more in the years to come. Properly situated, of course.