Unfortunately there will always be a color difference between the two.
When I get down to where there's only a couple feet left on a roll, or large enough pieces of scrap that would normally just go in the trash, I cut it off, roll it up and stick them in a box. When I need to do color matches/ color proofs I rotate em' 90 so they're long enough, stick em' in the printer I'll be using for the job. Waste doesn't go to waste, don't have to use what's on full rolls you need for jobs just for these things, and colors be accurate. I always have a few pieces of the most commonly used stuff for this. Doesn't take up much room, and off of standard 54" wide material you can get a quite a bit on a 24" wide strip, not just for proofs, but experimenting, testing profiles and other things, or just trying to match colors. You can waste a lot of vinyl trying to hit some colors, making a swatch or two, or even small decal proofs to show a customer. Been doing this for decades, and can't even imagine how many rolls of vinyl it's saved having to purchase, a foot here and there adds up to a lot over time. One man's trash is another man's treasure