I think that your latest code is not yet on Github.... your ranges are likely 0 = grey, 1 = green, 2-5 blue, 6-10 brighter blue, 11-15 bright red, 15-19 darker red,...
When you look at it, you might think that 6-10 colored segments have less travelers...
btw: It would be great to be able loading traveled graphs via option 1 in addition.