The fuel pump plug was my initial thought also.

BUT...

- the fuel pump plug is a rather intense green while this is more of a blue
- I doubt the bike would have functioned properly for more than 2.000km without an active fuel pump

Of course, safest bet would be to actually remove the tank an look for myself, but since the tank is almost full and Yamaha made sure the operation is as complex as it gets... said I ask around first.