The color deviation is already quite extreme. If the vinyl had been in use or had been in the party cellar where 15 people were smoking every evening, I would have said that it was the same. But batch deviations in vinyl aren't that extreme. I think the wrong color was sent to you. Do you know which manufacturer (Morben, Enduratex, Skai, ATN, Spradling etc.) the artificial leather is from? Some suppliers don't have the whole color palette of a supplier in their program but only a few selected colors. Then you could check it with the manufacturer of the vinyl. It is also possible that the supplier ordered wrongly or labelled wrongly.
At least I haven't had such a colour deviation with vinyl yet. With leather yes - but this is also a natural product and is usually pre-treated in the country of origin. And the colour variations that are as strong as yours are also quite rare with leather...that has been the strongest I have had this year:

@Jens Jesberg the swatch book just says soft impact for a brand name. I tried finding small print to see who it was made by. I feel soft impact is probably the collection name and not the manufacturer. But I agree, I feel the color is just too far off. I have to make the back seat so they won’t be right next to the front seats. But I think people will be able to tell still

I have just searched the name of the collection on the Internet and my guess has been confirmed. There seem to be different colour gradations of the imitation leather. I've seen that with vinyl produced in America, there are colour shades like "light oak" "middle oak" "dark oak". Maybe you'll get a different shade.
I wouldn't do the back seat like that. You have to discuss this with the customer beforehand. Or tell him that the vinyl for the front seats is no longer produced.
Or you take a vinyl that has the same color but a different grain. For example "Valancia" grain instead of "Milled Prebble". Because for the eye matching colour is more important than matching grain.
You could also ask Torrie Coffman for help. Albright's Supply has the Soft Impact imitation leather in its program.

@Jens Jesberg thanks for looking that up. It was Albright I ordered from but got busy on another project yesterday to get a call in. Hoping to call them Monday and see if we can’t get things figured out. I’ll see if I can’t find the medium color swatch in my book to compare.

I use the Soft Impact book all the time. It is the only book I have ever seen where what you see is what you get. Very little, if any color variation. I do seat repair, so it is very important that what I see is what I get. I have never seen material that far off in color, from that book. A mistake was made somewhere. It is very hard to find a supplier for Soft Impact. I get mine from Midwest Fabrics. You probably have heard of them, being from the midwest.

@Jim Bentley actually I just got an account signed up with Midwest fabrics. I’m about 2.5 hours away from the twin cities and lives there for some time. I think I’m gonna plan a day with friends and go to them, possibly pyramid trim too and see what I can come up with. I agree. Something isn’t right. But the billing invoice is all stuff for these seats and I can’t recall any other project with a color even close to this. So has to be that invoice.

Don't forget to take a swatch of those left-overs that you're trying to match with you.
Those damn "DoH!" moments, y'know? Lol!