Color lines by angle

Most of your lines are "multipoint" and your color function doesn't support them well. You can enforce "two points lines" by doing something like this (I'm following your map code styling here):

Show[Graphics[{AngleColor[#[[2]] - #[[1]]], Line[#]}] & /@ 
      Partition[#, 2, 1] & /@ # & /@ testD, Background -> Black, ImageSize -> 800]

But I would rather prefer this other way:

angleLine[x_] := 
 Module[{a = ArcCos[{1, 0}.Normalize[Subtract @@ x]]/(Pi)},
        {If[a >= 0.5, Blend[{White, Orange, Orange, Purple, Purple, White}, 2 (a - 0.5)], 
                      Blend[{White, Purple, Purple, Orange, Orange, White}, 2 a]], Line@x}]

Show[Graphics[Map[angleLine /@ Partition[#, 2, 1] &, testD, {2}],
             Background -> Black, ImageSize -> 800]]