The dark purple awareness ribbon is for Crohn's and Colitis awareness, at least in Australia. Both are diseases which as yet there are no cures for, and can be somewhat debilitating.
Both Crohn's and Colitis affect the bowel, and a person who suffers from either can spend the day running for the nearest toilet with severe diarrhoea. It is unpleasant to say the least.
Please help find a cure by donating to -
Crohn's and Colitis Australia ([link]
Crohn's and Colitis Foundation of America - ([link]
Crohn's and Colitis Foundation of Canada - ([link]
National Association for Colitis and Crohn's Disease - ([link]
or the organisation in your country.
For more info -
Crohn's Disease - [link]
Colitis - [link]