from matplotlib import pyplot as plot

def darken_adobe(s):
	if s <= .5: return .4
	if s >= 2.333: return 0
	if 1 <= s <= 1.667: return .275
	if s < 1: return .4 + (s-.5)/(1-.5)*(.275-.4)
	if s > 1.667: return .275 + (s-1.667)/(2.333-1.667)*(0-.275)
	assert 0

def darken_simple(s):
	if s >= 2.5: return 0
	return .5 * (1. - (s / 2.5))

def darken(xs, func):
	return [x+func(x) for x in xs]

xs = [x / 100. for x in range(0, 300, 3)]
plot.plot(xs, xs,
	  xs, darken(xs, darken_adobe),
	  xs, darken(xs, darken_simple))
plot.show()