It looks like you have a pair of black and white clownfish and not mocha clownfish. I hope you didn't pay top dollar for mocha clownfish, b/c it looks like they sold you black and white clownfish instead (although black and white clownfish can be pretty pricey also).
Black and white clownfish are born a mocha color (this is normal) and when they turn into young adults they loose their mocha color and transition into black and white clownfish. They may end up keeping a little mocha orange around the face for years before turning into full adults when they turn completely black and white.
In nature black and white clownfish are found in northern Australian waters.
Here are a couple pics of mine as they transitioned from mocha to black.
My two clowns were born October 2011, captive breed by a local reefer. They are 3 years old as of this past October. You will notice that they are not a true orange color as young of the year, instead they are mocha in color. The mocha color transitioned to black fairly quickly between 5-8 months old for these two. After that they had black and white bodies with orange faces. They have kept their orange faces until this past year. In year two the larger of the two lost her orange face and had a black face. The male as of today, at 3+ years old, still has his orange face. The transition of loosing the orange face happens slowly with the black creeping from the back of the head to the tip of the nose until only a little orange shows at the tip of the nose, then is gone.