Rosemary doesn't really need feeding as it naturally grows on rocky hillsides in the Med. But you could give it a light feed with a regular plant food. Another idea, though, check on the undersides of the leaves for insects. They may be sucking the plant's sap and causing the yellowing.

And check the pots to see how dry they are - the only time mine goes yellow is when I've forgotten to water, and mine's in a pot too.

Since they are in pots and can't go looking for nutrients, a light, slow feeding might be in order.