and white...
http://www.falsebayco.com/encounters...-shark-attack/
and blue...
http://www.sanluisobispo.com/2012/05...er-rescue.html
and red...
http://blog.austinkayak.com/2010/08/...-shark-attack/
Get what you like. Brighter colors can easily be seen by boaters/others, the color of your kayak probably isn't a factor in shark/kayak encounters (maybe there are more yellow kayaks than any other color thus a yellow kayak is likely to have a shark encounter). Just be safe and paddle w/ others