TernaryAxesSubplot.scatter() skips first default color in version 1.0.8 about python-ternary HOT 1 OPEN

Answer: The first color is missing in version 1.0.8 because of the addition of one additional function call in TernaryAxesSubplot class, ( Add functions for setting a ternary specific background color ). It calls self.set_background_color(), which intern calls background_color() from heatmapping.py (Please check out the __init__ in TernaryAxesSubplot). This background_color() function essentially creates the triangular region filled with 'whitesmoke' color, which you see in the background of your 2nd figure.
Now, let's go back to your code.

fig, tax = ternary.figure(scale=1) 
tax.scatter([(1.1/3, 0.9/3, 1/3)], label="first")
tax.scatter([(0.9/3, 1.1/3, 1/3)], label="second")
tax.legend()
tax.set_title(f"python-ternary {ternary.__version__}")
tax.show()

Apparently, it looks like you created the tax in line 1 and drew scatter after that. So, the first scatter call should be the first time something is drawn on your axis. But note, the ternary.figure() already called the background_color() function. So, you already drew the first drawing on your axis, and the tax.scatter() call is actually the 2nd time you are drawing something on the axis. That's why the 1st color is missing in tax.scatter().
You can easily check this if you comment out the self.set_background_color() call in __init__ in TernaryAxesSubplot class.

Solution: You just have to restart your color cycle.

import ternary
import matplotlib.pyplot as plt

fig, tax = ternary.figure(scale=1)
plt.gca().set_prop_cycle(None)  # restarts the color cycle
tax.scatter([(1.1/3, 0.9/3, 1/3)], label="first")
tax.scatter([(0.9/3, 1.1/3, 1/3)], label="second")
tax.legend()
tax.set_title(f"python-ternary {ternary.__version__}")
tax.show()

from python-ternary.