M3 nylon spacers fit over M2 spacers
Non-threaded M3 nylon spacers have a 3.2 mm inner diameter (ID) that fits over the cheap brass M2 threaded spacers. They come in two outer diameters (OD), 5mm and 7mm. The 7mm ones are most common but are probably too large for most uses. The 5mm OD ones are perfect for hiding the skinny brass spacers.They are sold on eBay and Aliexpress. They come in all the same lengths as the brass spacers. Amazon has some but they are in kits of mixed sizes, many too short or too long to be useful.
Since they are made of nylon they should dye very well.
These are much sturdier than regular all nylon threaded spacers, when combined with a brass spacer. You can tighten them much more as the brass spacer's threads won't easily strip.
5mm OD M3 nylon spacer next to a M2 threaded brass spacer.
M3 spacer on top of the M2 spacer. It fits well but is not snug. It will fall off if you flip the board over while assembling.
Installed and screwed in place. The raw nylon is translucent. Could dye them black or some other dark color. I have seen ones that are white nylon (more opaque) and some in black nylon.
8mm long 5mm OD spacers on a Dilly with plates.