Yes, TONE is a Scrabble word!

Letter values in Scrabble US: T 1, O 1, N 1, E 1.

Is it a valid word?

TONE is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the quality of a person's voice
(linguistics) a pitch or change in pitch of the voice that serves to distinguish words in tonal languages
(music) the distinctive property of a complex sound (a voice or noise or musical sound)
the general atmosphere of a place or situation and the effect that it has on people
a quality of a given color that differs slightly from another color
a notation representing the pitch and duration of a musical sound
a steady sound without overtones
the elastic tension of living muscles, arteries, etc. that facilitate response to stimuli
a musical interval of two semitones
the quality of something (an act or a piece of writing) that reveals the attitudes and presuppositions of the author

Also: tone of voice, musical note, pure tone, whole tone, whole step, tone up.