It looks like you have the Air-X 400, just like mine. Air-X recommends 5 year replacement schedule for an unknown reason.
I replaced my blades about 7 years- just because. I promptly had one new blade break and after I returned them the company said it was due to a bird strike- not covered by warrantee.
Well, I did not find a dead bird, feathers, blood, or any other evidence of a bird strike, but the bottom line was I had to buy another set of blades. Left a bad taste in my mouth.
If I ever buy another set, it won't be from Air-X. There are at least two other suppliers. One is half the cost of Air-X and the other is a European supplier who claims that his blade are virtually silent. But they cost 3X the price of Air-X. I think they are the blue ones to which you refer.
I don't know if the blades degrade due to UV, or why they need replacement. Maybe someone else has the answer.
But I will add that if any of these blades fail (and I do have some used spares) I will be very tempted to ditch the Air-X and install solar. When I installed the Air-X, solar was not as efficient nor as inexpensive as it is today,