Well I don't know if this is right, but if I had to guess

red-head scarf might suggest that the flairs at the end of the scarf are red, and that it just a normal scarf https://www.google.ca/search?safe=off&tbm=isch

where as a red head-scarf would be a red... head scarf. https://www.google.ca/search?q=head+scarf&tbm=isch

Dunno. Needs more context frankly.