oh man.. this fall under clients are INDEED stupid. it also reminds of a shirt a coworker got me (" I am only wearing black until they invent something darker").
Returning to client stupidity tho, remeber many clients don't know how to communicate what they are envisioning. It is possible ( since you considered "bolding" to be a possibility) that the client doesnt mean make it darker... but make it heavier or that the client just want higher contrast ( background lighter)
be aware of the potential problems with too high a contrast.
Namely, the negative impact it has on dyslexic readers.
which is a good point. but that goes back to client education..