I foresee a lot of philosophical discussion in the RBN wiki's future regarding blue representing open hi-hat, especially with songs like Down With the Sickness.
I personally love the blue mapping for open hi-hat. Using a Roland drum kit via the GH:WT MIDI port, I have mapped my electronic hi-hat pad to both yellow and blue. Yellow when closed, and blue when open. Allows for real world drumming, and works great.