I have only a few of these and discovered first to-day that there are two velvet seals set into the edges of the sleeve to reduce clearance and provide a non abrasive movement. These are present in serial numbers 11445, 16819 and 17142 and probably for a wider range of serial numbers.
There is only occasionally any reason to remove the sleeve - in fact it can be quite a problem with tangential drives as the brass screws have very short threads cut the barrel.
The basic colour of the velvet is (at least, now anyway) black. The lens I took apart had lost both the velvet seals and there was plenty of verdigris in the turned depression which needed to be cleaned out.
I have bad experiences with modern types of velvet material as the threads tend to come loose when cut to size. I found a reel of ribbon which behaves much more politely when cut.
Before and after photographs below.
Purple was the only reasonable colour available!