Could this be a lack of quality standard because of profits.

People I've known who've had both eyes done bought a cheapo pair for the duration between having the first eye done, and the second eye done.

AIUI: for plastic lenses at least, the tint is applied to the surface of the lens after it has been made; the degree of tint depends on the length of time the lens spends in the tinting solution, its concentration and temperature. There are many variables to consider which are not necessarily under the lens manufacturer's control, e.g. it may be the dispensing optician who applies the tint. It's hardly surprising that lenses made and tinted at different times will have different tints. I may be wrong (I often am) but I'm sure that if so, someone who knows better than I do will be along to correct me.

But if all steps are controlled then viariability should be minimal.

I wore no glasses at all between first and second one. Now with the second one done I've gone back to an older varifocal glasses until I can get back to the opticians to get a new pair based on my new eye lenses.

One should go back to the opticians to get the OK to drive again (I was off driving for 5 weeks after the first one), he said he didn't need to see me at all after the second as my vision with one eye was quite back to normal. There's no reason I can see to get glasses between first and second.

I didn't need any glasses between first and second because I then had one eye normal vision but no near vision, the other eye quite short-sighted. So everything was covered. Or so I thought. One thing I'd overlooked was that normally, each eye covers for the other where the blind spot is concerned. In the case where the left eye is now the one that can see distance, the blind spot is in a bad place where driving is concerned, so I scraped the left of the car a couple of times in an underground garage.

Once both eyes are done, wait for six months or so before going back to get a final set of glasses.

Just like 35mm film processing :-)

From the well pummelled keyboard of Archibald Tarquin Blenkinsopp Esq

"Should be" butters no parsnips; it depends on who is doing the controlling, among the other factors I listed. This ain't a perfect world, more's the pity.

So you would accept a different colour shade on a wing of your car.

maybe a shopkeeper will appear, as if by magic?

How long have you had the new lens? You may find that the difference becomes less noticible over time, they change slightly as they react until they 'settle'.

The photochromic effect is brought about by material (IIRC silver halides), either within the lens as a whole or applied in a film on the front. If you've got varifocals then they will be specific to a supplier and if there's only months in it there shouldn't be notable difference, it's not as if they make a pair from scratch, they are made in massive quantities, if you get a new pair of lenses there's not a lot to say that the blanks were made within months of each other anyway.

We might suggest replacing photochromic lenses in pairs but mainly when a fair amount of time has elapsed so we might not be replacing like for like (suppliers change their designs (Transitions for example are Generation 8), And unbranded stuff does change over time, Or where we didn't supply the original lenses so don't know what to order to match.

No, which is why you might have chosen the option of a whole car respray.

Haha, one did.

For solid tints yes,

Photochromic is a batch produced lens material.

Lots of stuff is made in batches and given batch numbers for traceability.

colour variance is one thing that is tricky to reproduce accurately with certain materials.

try getting a pack of bricks or floor tiles that come from different batches and compare the differences. Might be none, to quite obvious.