Hi
You should also consider that the dark blue texture is also the shore-line of a sea or one side of a wide river.
A google map of the area will put you straight.
Tiger Lines - (Texture colours)
Red = Roads, Big line = big road, small line = small road
Blue = Rivers, Shorelines
Black = Political Boundaries, (counties etc.)
Teal = Rail lines (light blue)
Light green = Small streams