You don’t necessarily need any other colors. Chocolate can just be bred to chocolate and will breed true.
If you're asking what colors you can breed to chocolate while you're trying to breed it in, I suggest black, as chocolate is technically just black with a dilution gene.
If you want to mix chocolate with other colors for a more colorful flock, you could mix in blue as well, which will create mauve (chocolate on a blue base). Paint can also be bred to chocolate, if you wanted chocolate paints. But as I said, it's not necessary to add any other colors to chocolate.
You cannot create chocolate from other colors that don't carry the chocolate gene, so you'll need at least one chocolate bird or a chocolate carrier to start with.
Here's a chocolate and black breeding chart:
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