Picture discs - Collectors items?

Hello...

I have an opportunity to buy a few dozen new, sealed picture discs - leftover inventory.

I have a few questions, please. I shall use the abbreviation PD to refer to them following.

Were PDs just a novelty and suitable only for memorabilia collectors? I realise that PDs were being released just at the beginning of the CD era.

Were PDs pressed from a superior grade of vinyl? I've seen them in different colours.

Does the colour of the PD vinyl make a difference in the sonic quality of the recording?

Were any PDs re-mastered at all? Again, this was at the time that CDs were being introduced and some recordings were re-mastered.

I am not looking to buy and then sell this stuff on eBay but to add to my collection.

Thanks and regards,

Jan