knobChanged nuke node color change example

# Run with a node like this selected:
'''
NoOp {
 name NodeColor
 addUserKnob {20 NodeColor}
 addUserKnob {4 node_color t "Set Node Color" M {red green blue yellow}}
}
'''

n = nuke.selectedNode()
n['knobChanged'].setValue('''
# nuke.thisNode()  returns the node that this code is running in
n = nuke.thisNode()
# nuke.thisKnob() returns the value of the current knob being changed when run as a callback
k = nuke.thisKnob()
# Only trigger the callback if the changed knob name is 'node_color'
if k.name() == 'node_color':
    # Figure out which color the menu was set to
    menu_val = k.value()
    if menu_val == 'red':
        color = (1,0,0)
    elif menu_val == 'green':
        color = (0,1,0)
    elif menu_val == 'blue':
        color = (0,0,1)
    elif menu_val == 'yellow':
        color = (0.5,0.5,0)
    # Format the color into the proper hex code that the tile_color knob accepts.
    hex_color = int('%02x%02x%02x%02x' % (color[0]*255, color[1]*255, color[2]*255, 1), 16)
    n['tile_color'].setValue(hex_color)''')