PROTOTYPE: Why go beyond the original design mock-up? That was the philosophy behind Yohji Yamamoto’s debut men’s and women’s sunglasses line, Prototype, made in association with Linda Farrow. The collection, featuring purist, work-in-progress-style functional forms and industrial details, was introduced in the house’s show on Monday. Sophisticated elements include clip-on titanium and aluminum colored lenses — in hues such as smoky brown, white and graduated blue and green — that provide contrasting layers of color. Chrome-coated frames come in a range of finishes such as white, black and brown. Prices have not yet been released for the line, which will be distributed to select retailers and Yohji Yamamoto, Y’s or Linda Farrow Gallery stores.