If there is tooth decay, is it always brown or black?

No: Incipient carious lesions are always white then turn yellow, brown and black.

Hard to discern.: While decay can be brown or black, staining from coffee, tobacco or foods may also look like decay. Furthermore, the majority of adult decay occurs "between the teeth" and can be difficult for even a dentist to spot without radiographs. Regardless, if your teeth are showing signs of dark stains, get them professionally cleaned and let your dentist then make a diagnosis.

Decay: Generally decay will be brown or black. Unless it is very early in the decay process, these areas can be a chalky white spot. These usually start near your gums on the front of your teeth or around ortho brackets.

No: No, the color can vary. Could bye chalky white, yellow, orange, brown or black.