http://imgur.com/a/12ISp

edges.py

#! /usr/bin/python
import Image

source = Image.open("less3.png")
img = source.load()

width = source.size[0]
height = source.size[1]

def total_color_difference(pixel, other_pixel):
  return abs(pixel[0] - other_pixel[0]) + abs(pixel[1] - other_pixel[1]) + abs(pixel[2] - other_pixel[2])

DIFFERENCE_THRESHOLD = 175 #  mess with this until it looks nice.

# find vertical edges
for y in xrange(1, height-1):
	for x in xrange(0, width):
		if total_color_difference(img[x,y-1], img[x,y+1]) >= DIFFERENCE_THRESHOLD:
			img[x, y] = (255, 119, 255)

source.save("edges.png")