Procedure 'spiral' draws a line, turns through a fixed angle, then calls itself with a line length 4 pixels longer. The result is a series of angled lines giving a twisted spiral effect.
# set default screen, pen and turtle values
ResetAll SetScreenSize [400 400] HideTurtle
SetSC Black SetPC Green SetPS 1 PenUp
To Spiral :Length :Angle
SetPC PenCol :Length # pen color depends on line length
If :Length > 390 # if line length too long ...
[Forward :Length/2 Stop] # draw half line length and stop
Forward :Length Left :Angle # draw line and rotate a fixed angle
Spiral :Length+4 :Angle # do again with a length 4 pixels longer
To Pencol :Length
Make "Green Round :Length/1.62 # green depends on length
Output ( List 0 :Green 0 ) # red and blue set to 0
For [Angle 158 176 2] [ # repeat 10 times
Wait 5 Spiral 1 :Angle Wait 200] # begin spiral with a length 1