I took the ferry to the five Islands close to Oslo. I noticed in particular that on Langoyene at least 90% of the houses were yellow and red. When asked the answer was that there is no particular reason for the predominantly read and yellow colors. That doesn't seem right to me!!!
In taking the trams and the buses today outside of downtown Oslo came across a great number of buildings that were red with yellow trim or yellow with red trim. So maybe waaaaay back when the color was significant period does anybody know?