Several sites discuss the bicycle manufacturer in some detail, but there is no evidence that they ever made motorcycles. It is possible however that they rebranded imported motorcycles. It has been suggested Vierkleur motorfiets were produced 1904 to 1906, but as the company was formed in 1905 this seems unlikely.
The company changed hands in 1912 and again in 1917. It was run by Witmondt until the Nazis invaded and, being Jewish, he was sent to Auschwitz and murdered.
rijwiel.net has a fair bit on the marque, and does mention motorcycles, but not that they actually built them.
shie.nl has a good timeline with several images. No mention of motorcycles.
The marque is mentioned in De Nederlandse Motorhistorie by Piet Cornet, ISBN 90 6013 664 0
