A white border means that at least one crossing should be open and safe.
It is possible to enter Colombia from both Brazil and Peru in Leticia in the very South, but the town is in the middle of the Amazon jungle and has no connection with the rest of Colombia except by plane. There is no border control so you need to find the immigration offices yourself to get passport stamps.
It is possible to walk across the border between Sapzurro, Colombia and La Miel, Panama but you need to take a coastal boat to get to/from either place.
It is technically possible to enter North Korea from South Korea in a place called "Joint Security Area" (you don't even need a visa), but you can't travel anywhere further.