
In a letter to Émile Bernard, from Arles, June 1888, in 'Van Gogh's Letters', http://www.webexhibits.org/vangogh/letter/18/B06.htm
1880s, 1888
Context: There is no blue without yellow and without orange, and if you put in blue, then you must put in yellow, and orange too, mustn't you? Oh well, you will tell me that what I write to you are only banalities.