What method is complex_number_to_cmap_rgb using to generate its values?

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Note: Throughout my question I will be abbreviating complex_number_to_cmap_rgb as ztc_rgb. This is not what you should enter if you want to test my code. Use the full and actual name, as I do not want people claiming I am using a non-existent method.

I have 2 questions rolled into 1:

1. What method is ztc_rgb using to generate values?
2. How is it impacting my code?

For #1, I have looked at the documentation for ztc_rgb on SageMath's reference manual (I am using version 10.0 in Ubuntu 22.04.2 on WSL). All I see is info on various ways of displaing argument and magnitude using contours and the like. I want to know what ztc_rgb is doing under the hood, as that ties into #2.

For #2, This is the code that I'm running, with f=np.poly1d([1,0,0,-1]) ($x^3-1$) replacing f=np.poly1d([1,0,0,0,1,0,-1]):

 import numpy as np
 f = np.poly1d([1,0,0,0,1,0,-1]) #x^6 + x^2 - 1
 fp = np.polyder(f)
 c = 700
 x = np.linspace(-1,1,c)
 y = np.linspace(-1,1,c)
 xx,yy = np.meshgrid(x,y)
 z = xx+yy*1j
 for i in range(8):
      z = z - (f(z)/fp(z))
 z
 n = z.ravel()
 n = n.tolist()
 from sage.plot.complex_plot import complex_to_cmap_rgb
 k = complex_to_cmap_rgb([n], cmap='plasma')
 b = k.reshape(c,c,3)
 plt.imshow(b)

I get blobs ($x^3-1$) and squiggly lines ($x^6+x^2-1$) in portions of the plot (unable to add images). Can someone tell what's going on, and how I can fix it?

Edit: I think I have fixed my 2nd question, however I will leave this question open for the first.