Sorry I don't have any MX250 or 450 to test, but it's the same fan module (MA-FAN-18K) as used on the MS350-24X and MS425 switches. If you have non 24X MS350, it's a different fan, the MA-FAN-16K. So while it's possible there's a difference in LED color codes, I'd check with Meraki Support, there should be some MX250/450 units around to take a quick peek. Please so report back if you get the definitive answer.