Ploting a list of points with different color that is determined by another list?

The usual imports

import numpy as np
import matplotlib.pyplot as plt

faking some data

labels = 'a b c a b c a b c'.split()
tuples = [(1, 2), (3, 4), (5, 6), (3, 2), (2, 1), (1, 0), (5, 1), (3, 1), (4, 1)]

you need a way to map labels to colors, and a dictionary is a mapping, isn't it?

color = dict(zip(set(labels), 'red,blue,purple,green'.split(',')))

next, you can plot the individual points with their color, with just a difference from usual stuff, you specify a zorder greater than the default value of 1 (the reason will be explained later).

for (x, y), label in zip(tuples, labels):
    plt.scatter(x, y, color=color[label], zorder=2)

Now, if you want to have a legend, you may be tempted to add a label=label to the previous statement, followed by a plt.legend(), but that won't work, because you will have a line in the legend for each of the data points.

You need to plot a single point for each of the different labels, with the correct color, the correct label and the correct size, and then call plt.legend (that now will do the right thing), but, at the same time, the auxiliary dots must be invisible.

This invisibility can be obtained plotting the extra points behind the last point, whose coordinates x and y are still known to the interpreter, using a zorder value less than what we used for the regular data points.

for label in set(labels):
    plt.scatter(x, y, color=color[label], label=label, zorder=1)
plt.legend()