I did a Google search using the phrase, "Colors that repel birds" and came up with some ideas.

Like when you are not sailing, turn your mast into a flagpole by attaching a retrieval line to your halyard shackle (or tie the halyard to itself to make it continuous) and use the halyard to hoist to the top of the mast a bright-colored balloon or a strip of bright-colored metallic tape that will wave in the breeze.

Products like this are actually available for the purpose of repelling birds, but you could probably come up with something yourself. Here are two links.

http://izola.co.uk/birds/products/itape.htm

http://www.gemplers.com/product/TEB/Scare-Eyes-Bird-Control-Balloon

Let us know what works.