"But most people think a microlight is a flexwing, not a C42"
Actually, I think you'll find that these days most 'microlights' are 3-axis. And if they did think it was a flexwing, well Cessna don't make those either. If you heard "Sleepy Airfield, G-CD downwind left hand 25" and then "Sleepy Airfield G-DC downwind left hand 25", explain how you'd know which one was which. On the other hand, if you heard "Sleepy Airfield, White Cessna CD downwind left hand 25" and then "Sleepy Airfield Red Piper DC downwind left hand 25" it's self explanatory.