Changing the color of already drawn brush strokes

I have a two layer image, with a map on the first layer, and many light blue brush strokes on the second (one such brush stroke is shown here on the left):

I wish to change just the color of the brush strokes on the second layer. while maintaining the look of the brush strokes.

I've tried using the paint bucket tool, and get this:

which causes two probems - the fading edges on the sides of the brush strokes are gone, and the original stroke with the original color is still visible below. Any help is appreciated.