The Answer Is A Foodstuff , 3 Letters.
Quizzes & Puzzles0 min ago
No best answer has yet been selected by David H. Once a best answer has been selected, it will be shown here.
For more on marking an answer as the "Best Answer", please visit our FAQ.Clearly, it is so called in photography/printing because it 'tones'...ie alters the black/white relationship on paper. I think you were just a bit naughty to query it, since it is certainly in both Chambers and the OED in addition to the OSW already referred to by Sft.
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