Theres definitely a difference and I know im in high gain. Purple is low gain at max volume pink is high gain. Ive been in pink this whole time, It seems theres a problem with my amplification but untill someone else tries using the zo2 with full sized headphones out of an iphone or ipod I wont know for sure.
I have an iPhone 4 and multiple generations of iPod. I can use them at about 65% volume and full sized headphones and it's honestly an uncomfortable volume level when in high gain mode! Please make sure your battery is fully charged, take it out of high gain mode, and put it back into high gain mode. This may solve your problem. When the battery indicator goes on, it automatically goes out of high gain and into low gain, but the lightbar stays pink. So you may think you're in high gain as per the lightbar color, but you may not be.