Brown lenses are a solid all-round performer and ideal if you own just one pair of sunglasses. Brown works well in mid to bright conditions and highlight things against green backgrounds. Brown lenses naturally filter out high frequency light waves and as a result have an image sharpening effect. They have a discrete anti-reflective coating on the inside and an extra hard coating on the outside to assist with scratch prevention.
They are also polarised for glare and because they perform well in both bright and dull conditions they are ideal if you live in an area that has frequently changing light condition such as overcast mornings changing to sunny afternoons.