Working HSV arrays, but low-pass not working properly yet
Fade working properly now, but might need brighter turn-on (low-pass effect in ON transition causes very dim and short tail)
Brighten more quickly than dim, to get a nicer tail; if tails overlap then mix the hue---otherwise directly use the head hue
Fading/interpolation now in HSV space: correct tail colour, at the cost of an extra LED array of 300 bytes. Overlapping tails could still use some improvement