Specifying Colors

In almost all places in matplotlib where a color can be specified by the user it can be provided as:

• an RGB or RGBA tuple of float values in [0, 1] (e.g., (0.1, 0.2, 0.5) or (0.1, 0.2, 0.5, 0.3))
• a hex RGB or RGBA string (e.g., '#0F0F0F' or '#0F0F0F0F')
• a string representation of a float value in [0, 1] inclusive for gray level (e.g., '0.5')
• one of {'b', 'g', 'r', 'c', 'm', 'y', 'k', 'w'}
• a X11/CSS4 color name
• a name from the xkcd color survey prefixed with 'xkcd:' (e.g., 'xkcd:sky blue')
• one of {'C0', 'C1', 'C2', 'C3', 'C4', 'C5', 'C6', 'C7', 'C8', 'C9'}

All string specifications of color are case-insensitive.

'CN' color selection

Color can be specified by a string matching the regex C[0-9]. This can be passed any place that a color is currently accepted and can be used as a ‘single character color’ in format-string to matplotlib.Axes.plot.

The single digit is the index into the default property cycle (matplotlib.rcParams['axes.prop_cycle']). If the property cycle does not include 'color' then black is returned. The color is evaluated when the artist is created. For example,

import numpy as np
import matplotlib.pyplot as plt
import matplotlib as mpl
th = np.linspace(0, 2*np.pi, 128)

def demo(sty):
    mpl.style.use(sty)
    fig, ax = plt.subplots(figsize=(3, 3))

    ax.set_title('style: {!r}'.format(sty), color='C0')

    ax.plot(th, np.cos(th), 'C1', label='C1')
    ax.plot(th, np.sin(th), 'C2', label='C2')
    ax.legend()

demo('default')
demo('seaborn')

(Source code)

(png, pdf)

(png, pdf)

will use the first color for the title and then plot using the second and third colors of each style’s mpl.rcParams['axes.prop_cycle'].

xkcd v X11/CSS4

The xkcd colors are derived from a user survey conducted by the webcomic xkcd. Details of the survey are available on the xkcd blog.

Out of 148 colors in the CSS color list, there are 95 name collisions between the X11/CSS4 names and the xkcd names, all but 3 of which have different hex values. For example 'blue' maps to '#0000FF' where as 'xkcd:blue' maps to '#0343DF'. Due to these name collisions all of the xkcd colors have 'xkcd:' prefixed. As noted in the blog post, while it might be interesting to re-define the X11/CSS4 names based on such a survey, we do not do so unilaterally.

The name collisions are shown in the table below; the color names where the hex values agree are shown in bold.

(Source code, png, pdf)