Use your white chocolate as is, or color it using oil based candy colorants (do not use water based colorants), or use colored candy wafers.
Using a decorator brush, dab the white/colored chocolate into the mold designs. After filling each design, tap the mold onto the table to settle the chocolate, and remove any trapped air.
Tip: If you are making many chocolate covered Oreos®, you may want to substitute the decorator brush with a squeeze bottle, or cake decorator, to facilitate filling the mold designs.