I’m not concerned about colour from the washing point of view.
Of far more importance to me, is to be seen on the road.
All my Jazz cars (4), have been in Milano Red, so as to show up on the road.
In my view, colours such as silver, grey, black etc all tend to blend in with the tarmac, making make them difficult to see, from a distance.
I recall many years ago, my first Austin Metro was bright Yellow, because at the time, the Fire Service were considering changing from red to yellow, so as to be seen under certain types a street light, of course that never happened, so for me Red it is.