It is not I think that the stone's tone is too dark, but there is extinction in the cut. The stone could very well be medium toned. But with extinction, the dark areas you see in the stone can become worse in brighter light.
Sunlight is great, but to many that live in colder climates forget that indoor light is more important, as you going to be wearing jewelry indoors under artificial light or mixed with indirect sunlight much more than you will be outdoors, especially in the cold months.
Really though, it is all conjecture. Stones are always best judged in person; you can only go by a picture or video (which is better) so far. Sure, it can give you an idea, but they are so many other things such as the light it was taken in how strong the light was, the latitude it was taken in if outdoors, the angle it was shot at can make a stone look darker or lighter, the body and camera always block some light which can also look like extinction. Many variables here.
Just make sure whomever you buy has a good return policy and that they write that into your invoice agreement if you go through Paypal.
Most vendors are honest, but there always that one...
