Noise of different colors can be generated on a Linux box with these commands (Ubuntu, Debian etc.):
sudo apt-get install sox
play -n synth 60:00 whitenoise
The latter command will generate white noise for 60 minutes. Also works with brown and pink.
#
Mikaela Mendoza: White noise machine are clinically proven solutions for looking for effective sleep aids.
dmitry: Awesome! I just looking for brownnoise. Thanks you very much.
GratefulMan: Thanks! This is certainly less resource intensive than flashplayer in a browser!
tb: Many thanks for this. It is also a lifesaver for people suffering from tinnitus (like me).
Diego Viola: Thanks, I'm currently using $(play -n synth brownnoise) instead of whitenoise, I find it more pleasent. I had problems with concentration/focus due to street noise, etc, and this is just a life-saver. Thank you so much.
John Spickes: This is now my favorite thing to listen to at work. Thank you very much for sharing it.
abelgard: Very interesting. How can I output it to a wav/mp3 file? Have tried various syntaxes, so far without luck.
Gern Blansten: I just organically created brown noise after a high-fiber meal. ;)
MuzSolutions: fyi, this program is a lifesaver. My fiance officially loves linux simply because of this whitenoise generator and can't sleep without it. She usually uses the brownnoise option though. ;) (if you omit the timecode (ie 60:00) and just type in "play -n synth brownnoise" it will play until you close the terminal.) If you use openSUSE you could install using "sudo zypper in sox".
transce080: Thanks this was really helpful in making a cheap white noise machine with a raspberry pi.