To me the G-15 lens is is a very classic and safe choice of color for sunglasses – Especially if you’re getting prescription sunglasses. The green-grayish color is soft on the eyes and looks very good in both metal and acetate frames.
In 1951 Bausch & Lomb invented the N-15 lens for the Navy Air Corps. The N-15 was later altered to be more suitable for prescription use.
The human eye responds more to green and yellow light than blues and reds. The G-15 lens emphasizes the wavelengths our eyes are most sensitive to and blocks the other colors. This gives you a natural vision without distorting the colors – it’s easier on the eyes.
The original G-15 lens is of mineral glass and blocks 85% of the light, which means it’s a dark lens since only 15% light gets through to your eyes. And of course the lens has 100% UV-protection.
Different lens manufacturers have different names for the G-15 color. Zeiss names it Pioneer, Essilor calls it . But Bausch & Lomb was first to call it G-15.
Photo from here.