Many blues that feed on flowering buckwheats camouflage themselves very well against the white or pink blossoms.  This is a spring azure (Celastrina ladon echo) third instar caterpillar feeding on host Eriogonum racemosum.  Other buckwheat-feeding lycaenids that camouflage themselves include Strymon melinus franki, Euphilotes spaldingi, Euphilotes pallescens, and others.