Volume to the face is fantastic, particularly for the pesky aging we get in in our 40s. One of my favorite places to inject is at the junction of the lower eyelid and cheek area.
HA fillers like Juvederm and Restylane need to be injected deeply around the eye. The skin around the eye is thin and almost transparent at times. If soft tissue fillers are injected superficially under the skin, there can be a bluish hue, called the “Tyndall effect.” 
I have my biases, and for injections around the eye I feel surgeons who operate around the eye know the anatomy better and are more comfortable with these deep injections. When I trained as a plastic surgeon, we do eyelid surgery. We fix facial fractures of the eye socket and cheekbone. It is nice when you are putting a needle close the eye to know exactly where you are.
Juvederm and Restylane are hydrophillic like all HA fillers. In English, this means it attracts water. This attraction for water combined with normal swelling (and/or bruise- to avoid bruise look at my blog on fillers) will give you some fullness which will go down.
You have to wait for a couple weeks after injection to figure out what is due to swelling from an injection around the eye versus what is the product. As all HA fillers, there is a way to reverse the product and essentially “melt” it away if you are unhappy with how it looks.
Some women have darkness of the tear trough for other reasons though– thin skin, vascularity, pigmentation, and shadow. This is not due to filler.