RCA 6SN7 grey bottles

https://imgur.com/a/aOhKIPf

How do they sound ? 

They seem to sound fine, for now.  But if there are better visually matching pairs available wouldn’t you rather have those instead?   

@baaach 

I have quite a few of the RCA gray glass, both the military VT231 and civilian 6SN7 versions. They vary somewhat in color and in density of color. I am using a pair of the VT231's along with a pair of black glass Kenrad VT231's in my preamp now. The Kenrad pair that I'm using is similar in appearance to some of the RCA's in that one is more gray and the other is a solid black. They test identically and sound great. It is about the sound but if it bothers you, there are plenty of them out there for you to make up pairs that match perfectly. 

@billpete , Thanks for your share as I don’t use that particular tube. To the Op , I would definitely prefer a better looking pair especially with equipment that has them prominently displayed. I did most of my tube purchasing about 10 years ago when I got back into 2 channel and tubes. At the time I was able to try many brands due to lower cost and stock up on the ones I preferred. Unfortunately for me the tube preamp I acquired recently takes 8 - 6H30p tubes and nos are $$$. If I were you and you like the gear and those tubes, buy a nice matching pair and keep those for spares. Maybe I’ll see you at Tube Addicts Anonymous . 😆 Merry Christmas , Mike B.