The differences are apparent right from the bottle, though. I had hastily thrown Indian Summer onto my swap board for about a week in a frenzied effort to get a hold of polishes I really wanted. I took it off right after swatching, ha ha. I need both, the end.
These are 3 thick-ish coats with Essie Good to Go on top. Artificial light, all of 'em.
You'll immediately notice the difference in the range of shift. I mean, these pretty much don't look like they're even in the same, like, class together at this point.
At least on the nail they look like they could be cousins. Cygnus Loop is much more blue-toned purple than Indian Summer, and it's less saturated. *Edit: "The difference is in the finish I would say, where ILNP is more metallic and Crowstoes is more like a thin jelly". Yeah! Thanks Ashley Rose Jordan. :)
Indian Summer shifts violet through magenta, red and stops just short of orange while Cygnus Loop goes right on through to bright gold.
I guess I should mention that in darker lighting, the difference really is pretty small. But that's irrelevant, because duh.