As for colours – this will have to be very carefully thought out to keep them distinct. Probably some lines will have to be a combination of colours (eg red outline with blue infill). It's still going to get messy at different scales. And as a colourblind friend says, "Will it work in greyscale?"
I have problems differentiating the existing range of colours, so they are going to have to vary texture (dashed, filled, etc) as well for some of us to have a chance. Quite challenging with the pocket Tube map.