Forever 21 from yellow to pink

So I was shopping in SF with my friend who is not interested in branding whatsoever. But even she noticed something I was definitely already thinking about while we were shopping downtown. For several years (I recall) Forever 21, the clothing store, has been using bright yellow solid colored bags with black letters along the bottom. Just recently they switched to a neon pink clear bag design with the same black letters. However my friend asked me the same question I was thinking in my head at the time. "Just why did they switch from yellow to pink?" I guess pink is a more feminine color and the color is also very bright. But why yellow in the first place? Maybe the company might switch to a bright solid or clear green in the next couple years? Was the company simply tired from the original color? Or did they assume people were getting tired of the yellow color, but not of the overall layout and size of the bag? I wonder how much research retail companies such as Forever 21 and H&M or Urban Outfitters conduct to determine whether or not they need to change their shopping bag designs, or do they simply feel intuitively when or if they should from time to time. There are companies who do change their designs more frequently then others, but I wonder just how frequent companies should change their designs, when thinking about catering to changing tastes while maintaining brand consistency. Forever 21's color change is definitely not as drastic as let's say, Tropicana's change, but it was definitely enough to catch my friend's attention, and I'm sure others as well.