This is the 15772nd most frequent Turkish word.
tonunu
"The tone of it."
In this context, 'tonunu' refers to the tone or pitch of one's voice.
Bana konuşurken sesinin tonunu biraz alçalt.
Lower your tone a bit when speaking to me.
Here, 'tonunu' is used to describe the shade or quality of a color.
Bu resimde renk tonunu çok beğendim.
I really liked the color tone in this picture.
In this usage, 'tonunu' implies the manner or attitude conveyed in one's criticism.