The color of the lens of these shades do not matter much unless it stands in stark contrast or is almost of the same color as the skin is. In either case, the extremes should be brought to moderation by choosing a color that goes with your skin tone and does not exhibit a sharp or a nil contrast.
If you have a round face, then opt for a rectangular frame. This frame does not draw attention to or compliment your face shape; it simply draws attention towards itself. You can choose the frame color from amongst a variety of colors including deep red to jet black.
However, if you are fair, is only when you should opt for these colors. Wear and check to see whether they match your skin tone. Then you must choose the color of the lenses.
If you are fair, then opt for a darker color amongst dark gray or black. In either case, let the frame be in the same family of colors. Do not wear round or oval framed shades. They will look best only on a square shaped face.
A square shaped face means that the length and the breadth of the face are the same. If you wear shades which are round or oval in shape, then they will be a contrast to the shape of the face and the shades being rounder will make your face look sleeker as the frame will help soften the jaw line.
The color of the lenses once again abides by the same principles as discussed earlier. Therefore the rule of the thumb will be to wear and see if the color of the lens suits you.
If you have heart shaped face then go for wide frames and if you have an oval shaped face, then you are lucky. Try out all the shades that there are, all will suit you. You just have to find the best.