ngrams
言葉の色	15
http://renso-
ruigo.com/word/%E8%A8%80%E8%91%89%E3%81%AE%E8%89%B2
"言葉の色の類語、関連語、連想される言葉
　・　言語げんぎょ　・　言葉振り　・　言葉遣い"

I guess this is covered by いろ【色】②㋒ in daijr:   （声
などの）調子・響き。 「声こわ－」 「音ね－」 or ７ in daijs: 
"音・声などの響き。調子。「琴の音(ね)の色」「声(こわ)色」"
Doesn't seem quite common enough to warrant its own 
entry.
I'll see if our 色 needs to be amended. 
Thank you for the suggestion, Fred.