Python. Color coding elements for scatter plot

You can set the colour of scatter plot points using c=... in the call to scatter:

import matplotlib.pyplot as plt

x = [1, 2, 3, 4, 5]
y = [10, 11, 12, 11, 9]
z = [2, 4, 4, 1, 1]

fig = plt.figure()
ax = fig.add_subplot(111)
ax.scatter(x, y, c=z, linewidth=0)

plt.show()

To give each point its own colour simply use range(len(x)) for the colours:

x = [1, 2, 3, 4, 5]
y = [10, 11, 12, 11, 9]

fig = plt.figure()
ax = fig.add_subplot(111)
ax.scatter(x, y, c=range(len(x)), linewidth=0)

plt.show()

Looking at the plt.scatter documentation, one finds that the c argument can be used for setting the color of the scatter points.

c : color, sequence, or sequence of color, optional, default: ‘b’  
    c can be a single color format string, or a sequence of color specifications  
    of length N, or a sequence of N numbers to be mapped to colors using  
    the cmap and norm specified via kwargs (see below).

So, in order to obtain a constant color for each scatter point, there are two options:

Specify an absolute color

plt.scatter(x,y, c=["blue", "red", "green"])

Specify a value to be colormapped according to a normalization

plt.scatter(x,y, c=[3.4, 5.6, 7.9, 1.0], cmap="jet", vmin=0, vmax=10)

or using a Normalize instance

norm = matplotlib.colors.Normalize(vmin=0, vmax=10)
plt.scatter(x,y, c=[3.4, 5.6, 7.9, 1.0], cmap="jet", norm=norm)

Without the normalization, the colors from the colormap would be distributed according the the minimum and maximum value in the array that is given to c.