This depends on the country. For example, in Australia, signboards generally have green backgrounds. Brown backgrounds indicate tourist destinations, and there are also those with blue backgrounds. In other countries, the speed limit sign might have a white background, while signs indicating works on the road may have orange backgrounds. With such a variety of colours, it really depends. Black is probably not used, as it it hard to see anyway.
Blue
Road signs on the motorways are blue with white writing.
Red . On all the many OS maps that I have, motorways are blue.
In the UK it is an emergency diversionary sign for motorways and primary routes.
you put tar on the road
Round signs give orders, normal triangle signs give warnings and rectangular signs give useful information (the background colour of these describes the road by the way).
26% in the UK.
It means an 'A road', the country's main roads after the busiest, the Motorways.
because people cross the road more in built up areas but dont on motorways
No that road is free and rel;atively trafic free compared to UK Motorways
white is the colour which we can see from the maximum distance and red is a alert signal or danger signal and has good reflections also.
In Britain roads are classified as Motorways, A & B roads & unclassified. Before the motorways were built A roads were the major Trunk roads which connected towns & cities in UK.
Danger signs are always triangular, on any roads and motorways in France.