special paint tips?

[Digger]

SO i have 2 different helmets I started with a beautiful Altman helmet, but later i bought an RS props red label, they both have been painted white.

The RS props is my 'go-to" costuming helmet, because it fits my tiny head best, soits been seeing a lot of sunlight, the other one however stands on display, not in direct sun, but it's a year older.

The RS props however is still spanking white after 50+ troops in it, whilst the other one has yellowed quite a bit waiting in the dark.
Is this normal with RS helmets, or is some other force at work?

Howcome it hasn't yellowed out yet? are there special white paints that prevent yellowing out?
While you're here, do you have any other tricks to prevent our nice white armour to stay white for a long time?

[Chopper]

What you're asking is essentially a chemistry question. In general, anything white has a risk of yellowing and discoloration over time, even if it's not in direct sunlight. 

It can have something to do with the specific paint used, or it can have something to do with any clearcoat that's used on top of the paint. There's really no way to know in an absolute sense, just that's there's probably a difference in the types of paint used on each helmet.

And there's no permanent way to proof something against yellowing, only that a lot of sun exposure will certainly accelerate the process. But as you've experienced, sometimes items will start to yellow regardless.