How something white turned black, and then white again. Schoonhoven was not averse to experimentation. Sometimes with exceptional and unexpected results.
Since the late 1960s, Schoonhoven and artist-friend Jan Henderikse had been faithful correspondents, sending each other letters and postcards about life on their respective shores of the Atlantic Ocean – Henderikse moved to Curaçao in 1962, and to New York in 1967.
A letter to Henderikse from February 1979 offers the first sign that Schoonhoven’s work seems to have reached a turning point. After almost 20 years of monochrome white reliefs, there was room for experimentation:
"I’m now in the process of trying to make a couple of small black reliefs (coming close to Ad Reinhardt’s territory). Whether they’re any good remains to be seen." 
Since the late 1950s American artist Ad Reinhardt had painted grids and compositions based on crosses in shades of grey, dark blue and black, compositions that were exceptionally reductionist in character.
It is somewhat ironic that Schoonhoven referred to Reinhardt in particular. As early as 1953, in his essay ‘Twelve Rules for a New Academy’, Reinhardt had stated his aversity against the use of 'non-color' white in visual art:
"White is antiseptic and not artistic. It is appropriate and pleasing for kitchen fixtures, and hardly the medium for expressing truth and beauty." 
It is unclear whether Schoonhoven was aware of Reinhardt's essay, although in the case of the black relief, Reinhardt’s influence seems to have extended beyond the dark surface. Schoonhoven’s black (now white) relief R80-2 (1980) has the shape of a double cross, clearly related in form to Reinhardt’s compositions.
But the most striking thing Schoonhoven's letter appears to show, is that in 1979 he seemed no longer fully committed to the programmatic significance of the non-color white. And yet these doubts were short-lived, as history shows us.
Notes:  Jan Schoonhoven to Jan Henderikse, 7 February 1979, archives of Jan Henderikse, New York.  Ad Reinhardt, 'Twelve Rules for a New Academy', in: Kristine Stiles and Peter Selz (eds.), Theories and Documents of Contemporary Art. A Sourcebook of Artists' Writings (Berkeley/Los Angeles, 1998), p. 88.