We, Canada, allow red rear indicators because the Americans allow them. No more reason than that.
I am sure that the Americans allow them because at some past time the Big 3 argued that they were cheaper than amber. Less wire, fewer bulbs and only one colour of glass ( plastic nowadays of course)
I have looked for and not been able to find any statistics that show that red is a safety hazard... whatever I/we may think and believe... so the chances of getting our regulations changed is about zero.
The thing that annoys me most is that the euro manufacturers , BMW and VW for example make specific Red rear lens for NA when in their own country Amber is the rule. To add insult to injury they are not even consistent about it.
AS for the actual topic. When we used to go to France every year we'd see the police on the autoroutes specifically checking that "stuff" bicycles or whatever did not obscure the rear lights on cars... they checked for overloading as well. More people than seatbelts and overloaded roof racks. They stationed themselves around toll booths and at rest areas to do this. Very sensible I thought.