A capsule for containing a chemical coloring agent as it treats a lock of hair has a male side with a projection and a female side with a cavity, connected by a hinge that allows the projection and the cavity to be swung into sealing relationship with the hair trapped therebetween. A reinforcing pattern of interconnected elements form a region of one of the surfaces, the pattern forming an array of spaced-apart islands. The interconnected elements provide enhanced rigidity for the capsule and provide the capsule a better grip on the hair to maintain the capsule in place. The male side and/or female side may be provided with a trough positioned opposite the hinge to reduce overflow of the coloring agent, and can be provided with a well positioned near the hinge to allow the hair to more readily distribute itself when folded over.