It is hard to say which color is bad for eyes ,different colors have its own effect in different situation .So some colors are less effective than others in certain situation . Black or grey lenses are suitable for: road rides even on sunny days.but not for mountain biking. Brown lenses are suitable for: mountain biking, not for night riding. Amber lenses are suitable for: mountain biking on cloudy days and on dimly lit trails, not for sunny days. You can see more detail information at this site :http://blog.firmoo.com/tips-for-selecting-proper-sunglasses-lens-color-for-different-riding-conditions.html
It depends on how you use it because different environment require different colors for sunglasses lenses. For example, grey or dark work for almost all outdoor sports in bright sunny days. But if you in low-level light condition, dark or grey color sunglasses are bad for eyes. In such low-level light environment, yellow or orange color sunglasses may be good choices because they can enhance contrasts in tricky, flat-light conditions thus to give you clear and comfortable vision.