Interestingly, when I started fishing a local shallow loch with the fly I was catching loads of fish on fluro orange, bright yellow and..yes..Pink large flies. This lasted a season. The following season was slower on the bright flies and really tailed off at the end of the year. The third season, I really struggled, until I switched to black or dark green flies...and so the patten repeated.
The same thing has happened to friends fishing large jerkbaits. The fish went made for them, then tailed off, a change to smaller jerkbaits, they came back, and tailed off again.
Seems Pike learn to associate certain colours/size of lures with danger after a while.