This is an overreach in respect of the trademark, a trade mark can be a shape a range of colours in a specific pattern or any other such thing however they must actually be using the trademark and in any dispute a court will look at what honda is using and what the flightgear folks have crated and then secondly look at what potential damage may have been caused to honda in respect of competitive activity as in both cases the answer is going to be no damage I cant see this being a strong enough case to attempt to bring to court,