If you exclude the ridiculously quick reaction times (which are likely down to chance), I think there must be a "lowest possible limit", going by nerve conductance velocities and suchlike. I.e. the optic nerve has to first inform the brain that the colour change has taken place, then the brain has to send out a signal to the muscles of the mouse-clicking-finger to make it click the mouse... Maybe I should try to work it out. I forget the upper conductance limit of neuromuscular nerve fibres... I know it's quite high...
I got an average of about 0.22, by the way. (that was when I didn't get overexcited and press "stop" too early...
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