That is "technically" true, in order to achieve that without replacing one of the present saber colors, you need a client side mod that replace high numbers, i.e. In that screenshot I was using 'color1 11', present colors are from 0 to 5, 6 is the jap custom colored one, 7 to 10 the custom blade jap ones and 11 the black one. I'm currently testing that placing the clientside files of ja++ at base just works, haven't seen any issues, except that obviously the custom colors doesn't work (plain white), since the server doesn't know that info.
From what I saw, server knows the client color1 (even if it a number outside of 0-5) and sync that with others, so a clientside mod that just adds more saber colors can be done, and other people who want to see those colors and install that mod can see those sabers on others too.
But well, this is a little off topic, I was thinking about posting this elsewhere.