These purple Marc Jacobs The Sweatpants cotton track pants are part of the label’s Colour Collection, designed to celebrate comfort, self-expression and creativity. Cut for a relaxed fit, they have an elasticated waistband and cuffs, logo patch pocket, tab detailing to the rear and logo lettering on the front hip. The brand calls this shade ‘purple potion.' Well, we're totally under the spell of these Marc Jacobs track pants.