ShonTron
Moderator
or just use a different colour between the 400 series and highways (i.e. 7, 12, etc). Why are all the highway and expressway symbols in Ontario black and white?
Actually, most US highways have black-and-white shields, including the US Routes. California's and Vermont's state highway shields are green, and a few other states, like Minnesota and Colorado, have some colour, but most are simple black-and-white rectangular signs with a simple circle, square, or diamond shape, or the outline of the state or other simple symbol (like New York's shield, Pennsylvania's keystone). You can see them all here: https://en.wikipedia.org/wiki/Numbered_highways_in_the_United_States
There's a little more variety in Canada: British Columbia's shield includes the provincial flag, Quebec has distinctive shields for both Autoroutes and Routes. Nova Scotia has attractive 100-series highway signs.
https://en.wikipedia.org/wiki/Numbered_highways_in_Canada