Turning white is OK, they will still work fine. No problems until they turn a dark yellow, and yes that will eventually happen. The Vifa divers are a poor replacement. Every thing is wrong about them, except that they physically fit the hole, and look OK.
There are silicone based replacement domes for them are difficult to mount into the polydome frames as you need to bond the new dome to the voice coils, AND get them properly aligned in the magnet gap... The seller has a gig for this; we do not. Still, if the domes go you have few options. If concerned that yours will fail; I'd suggest buying a set of his(get the clear ones) and keeping them for when the poly domes finally bite the dust. Those are on eBay.
I used domes from a set of B&O speakers, s-120 I think? They were made to the more similar design, but also have a slightly different impedance. You can put a resistor across them to match the original drivers, and tinker the pot. for that driver on the back. They sound very very close. Trying to find those drivers though are also tough. They should last much longer than the originals, simply because there was no internal coating on them. It's that internal coating that causes the domes to fail, as it both absorbs moisture, and is makes the domes more prone to UV degradation as well. I'd assume the internal damping was applied to remove some resonance problems, but perhaps the ones B&O used and which were seemingly the same as used in later models from Infinity were damped better to start with? In any case, this works and sounds good.
Since yours have not gone bad, yet, you have time to look for replacements, and consider your other options - like selling them to me for scrap parts..
