Layer on the acrylic paint, covering the entire piece (except the clip) with two or more coats of yellow. The metal will be visible through the paint until you have built up a few layers of paint. Next, paint brown spots on his front and back, and paint the front of his ears with a little brown. Paint his eyes black.
Let him dry, then coat him with a clear enamel spray to make the paint shine and improve durability. Be sure to tape off the clip, as the clear coat will probably chip off it when you flex it open.