I've been tying tube flies on those for a long time. They come in a lot of colors also. I have blue, purple, pink, mint green and white just off the top of my head. By the way don't anyone run out and buy a bunch of these, I got the big boxes of them and have about a 12 lifetime supply. I'd be happy to share. Here's another cool tube fly I did on those;
Ear plug poppers.
By the way, if you know someone that uses oxygen, the tube for the oxygen tanks fit these tube perfect. Ask them to save their old ones for you.