Blue lenses help enhance contrast and the most important aspect is that they protect our eyes from the harmful rays of the sun. Green lenses help with the contrast and cut down on glare. Grey lenses help reduce sun glare.because grey is a neutral color. Black lenses are the best for doing activities in very bright sunshine. On the other side, black lenses canÃ¢â‚¬â„¢t help contrast so much.
If you search clip on eyeglasses (clip on sunglasses) online, you can find there are many clip on sunglasses. Here are some online shop that you may find clip on eyeglasses: http://www.framesdirect.com/framesfc/Magic_Clip-lamckf-pr-l.html
Since you have had your eyeglasses, you'd better take your eyeglasses to some optical shops. Maybe you can find nice sunglasses clips that fit your eyeglasses. If you want to buy a pair of clips online, the size of the clips and eyeglasses may have some differences. This may make your eyeglasses look ugly too.
I think it might be difficult to find out a pair of clip-on lenses that fit your eyeglasses properly. If you have had that kind of clip-on lenses, you can take them to an optical shop and ask the optician to make a pair of eyeglasses for you. I don't know whether the eyeglasses stores will only sell a pair of clip-on lenses or not. So I can't give you any suggestions. But I think the easiest way is to ask the customer services online if you want to buy a pair of clip-on lenses online. Hope this helped! Good luck!