Dont know. Ive observed a lot of MH airplanes and travelled in some over the years and i recall the ones Ive seen seem to be always dirty on the outside.
Pollution + rain in 30 degree heat seems to make planes based in SEA pretty dirty. SQ Planes occasionally look like that and so do CX planes in the Summer.
Join Australian Frequent Flyer (AFF) for free and unlock insider tips, exclusive deals, and global meetups with 65,000+ frequent flyers.AFF members can also access our Frequent Flyer Training courses, and upgrade to Fast-track your way to expert traveller status and unlock even more exclusive discounts!