getDefaultColor

colour.py

node = nuke.selectedNode()
prefs = nuke.toNode('preferences')
allPrefKnobs = prefs.allKnobs()
colourClasses = [knob.name() for knob in allPrefKnobs if "NodeColourClass" in knob.name() ]

foundClass = ''
ruleFound = '' 

for colorClass in colourClasses:
	rules = prefs[colorClass].value().split()
	print rules 
	for rule in rules:
		if rule in node.Class().lower():
			ruleFound = rule
			foundClass = colorClass

print node.name()
print "Class " + foundClass
print ruleFound

if foundClass != "":
    postfix = foundClass.replace("NodeColourClass", "")
    colorValueKnob = "NodeColour%sColor" % postfix
    #print colorValueKnob
    print "Color: " + str(prefs[colorValueKnob].value())
else:
    print "Default color: " + str(prefs['NodeColor'].value())