Slightly embarrassed as I’m still in the process of gathering together modules for My First Eurorack, but along the way, the various iterations I decided were definitely - absolutely - for certain - going to be the final layout (they never were, of course!) occasionally called for blank panels.
The one constant in my rack design has been white/silver, from case to modules, and I was much taken with white options of these from Modular Synth Lab:
https://modularsynthlab.com/product/eurorack-blank-panels-3u/
They’re based in the EU, which may not be good for some Liners but I’m really please with the two I bought. Even though I probably won’t use them in my current planned layout… It doesn’t hurt to have spares, in case of future module reshuffles, right? 
If I was a black-rack kinda gal, then I’d definitely find a space for one of these plague doctor blanks from Ritual. I mean, in this year of the plague, how could I not?!
As an aside, I would like to see a bit more variety in 1u blank tiles - at the moment I’m looking to fill a 4hp gap and, while I’m very grateful for the Intellijel range, it would be cool to see something a tad more decorative!
Oh, and silver M3 knurlies, but that’s probably for a different thread! 