Primary colours an update.

I knew my musings on genera which have pure-coloured flowers in all three primary colours would produce an informed response. One customer scored with Primula, Meconopsis and Corydalis (google ‘red corydalis’ under images if you are sceptical), and two pointed out that Penstemon pinnifolius has pure yellow flowers. Nobody, however, has identified the Vinca http://jackdawsfield.blogspot.com/2008/04/help-vinca-major.html