Jesse, my first large macaw, was handled in towels from an early age, so she accepted them, would happily "step up" on them and would allow me to drape one over her, etc. No worries.

We had white towels, green ones, brown, etc. Never a problem.

But one day she encountered my bright purple beach towel  - and oh, my... she was terrified. She saw me lifting it from the laundry basket - screamed and ran off. She wasn't afraid of other things that colour, and as I said, she wasn't afraid of towels. Just this one towel.  No matter what I did to calm her, she remained truly afraid of this one towel.

So we started calling it "The Purple Towel of Death". 

It came in handy.

When we had brand new replacement windows (VERY expensive...) Jesse quickly formed the habit of climbing onto the windowsill next to her cage and happily mangling the vinyl edge. I could see a bad habit was forming, so I removed her and draped the "evil" towel on the windowsill.   As long as that towel was there, she stayed off the sill.  I left it there several days so that she fell out of the habit of going there every time she had her freedom.   When I took the towel away, she still occasionally went to that spot, but it wasn't automatic anymore.

From that point on, if Jesse developed a fascination for anything that was verboten, we'd simply apply The Purple Towel of Death and she'd leave it alone.

So far Laka (our B&G) just doesn't seem to have any specific items that she's consistently afraid of, but you can bet I'm on the lookout.