That looks great, where did you get those from?
Whilst loads of places do patterned decals I looked hard and low on the internet to find black only decals, and could only find a couple of places that did, neither of them as cheap as pattern decals. So, the ones I have are from signature custom designs and they are (usually) a very pretty penny, especially when you include postage - I almost felt guilty at spending the amount they ask, simply for decals.
However, if you act now they have their decals and protective films on black Friday deals and so at more palatable prices
https://www.signaturecd.com/
Search on Accessories/Side Panniers and Accessories/Top Box – the black versions are on the second page or so. The total cost under the black Friday offer is still a hundred quid for panniers plus top box but, I have to say, they are quality – not only you can work them a long time to ensure they are aligned and that bubbles are removed, but they also have a really nice matt finish. I wasn't disappointed, they almost look molded on. As always, patience gets results (I simply tackled one box and took a break before doing the next - they all came out very well).
And (I've checked), you can also use the 15% discount that Nutty negotiated with the company in conjunction with the Black Friday price – runs until Monday, 30 Nov.
UKGSER
(Thanks Nutty!!)
https://www.ukgser.com/forums/showthread.php/408573-UKGSER-discount-at-Signature-Custom-Designs
To add, their customer service seems quite good. I was concerned that one of the decals had a crease in when I got it, so dropped them a note - they responded almost straightaway explaining that it would come out when you rub your fingers over the decal but if a problem then to let them know. I found the best way was simply to use my fingers, not a protective film tool, as this did the job and ensured no damage to the film. You have to bear in mind that they are simply decals, and so they have to be treated with some care still - in this, they cannot match the alternative of powder coating.