I have several watercolor/pearlescent paintings on the black stonehenge aqua coldpress and am thrilled with the effect, however I tried sealing them with clear sealants and they kill the blackness of the paper, turning it greyish, regardless of how lightly I spray the sealant. What do you recommend to protect watercolor on this paper?

Most protective sprays will leave a matte finish to the painting, thereby diminishing the black color of the paper. However, you can apply a clear gloss varnish. You may not like the gloss appearance of the varnish, but it will protect and seal your painting. Try the Golden Watercolor Varnishes. Here's some more information:

https://www.goldenpaints.com/technicalinfo/technicalinfo_varnwatercolor#:~:text=If%20the%20watercolor%20is%20on,to%20prevent%20bleeding%20or%20streaking.

You might also want to try Krylon Crystal Clear UV spray. We have not tested this on the black paper, but it might be worth a test. Let us know how it performs.

One final note: If you're framing your work or keeping the panting safe in a flat-file, you really don't need to apply a sealant,

Have you tried using Dorland wax ?

I have used this on white and off white Arches, and it seems to keep the colors true. I don't know about black paper.

Use sparingly, or it can dry unevenly.