1. Spoken in low voice or a hushed voice.
Example: " Let's go out and eat today without's mother's knowlegde", said Amy, in a hushed voice(In an undertone), to her brother.
2. A Pale subdued colour- Though she recovered after her illneess, her skin still looked pale (Her skin had an undertone to it).
Overtone: an ulterior implicit meaning or quality.
Example: " You look very pretty today", praised Amy with overtones of envy.
"I should have listened to her" , he said with overtones of despair.