The study is comprised of two parts. The first portion of this study will be a double-blind, Sponsor-unblinded, vehicle-controlled study with application of INCB018424 or vehicle to paired lesions at least 15 cm apart in patients with active but stable plaque psoriasis. Part 2 of the study is a double-blind, sponsor unblinded, comparison of INCB018424 with two FDA approved products in patients with active but stable plaque psoriasis.