I think it's easy to make a flashing light pattern / color that doesn't resemble an emergency vehicle. That's why they're not illegal. There are actually precise rules governing what kind of lights you can get, at least in the US.
Now that I think of it though, I understand that having lights that don't resemble emergency vehicles in every country is difficult and customizing the lights for every country might drive the prices up. They might sell pre-made kits though. If I could have a kit made by Honda that would perfectly fit my bike so that it's just plug and play, i'd buy it. They could even have the system ready on every bike, minus the light bulbs. Then, depending on your country you buy light bulbs that don't resemble emergency vehicles.