Customizing color

Introduction to Data Visualization with Plotly in Python

Alex Scriven

Data Scientist

Customization in general

How to customize plots:

At plot creation, if an argument exists (like color)
After plot is created use update_layout()
- Takes a dictionary
- fig.update_layout({"title":{"text":"A New Title"}})

Why customize color?

Customizing color can help:

Make plots look awesome!
Convey analytical insights
- Color in this scatterplot adds a 3rd dimension.

Color as species

Some color theory

Computers use RGB encoding to specify colors:

RGB = A 3-digit code (each 0-255) mixing Red, Green, Blue
- (0,0,255) is blue and (255,255,0) is yellow

See more in this article

table of RGB color examples

Specifying colors in plotly.express

color argument (DataFrame column)
- Each category gets a color (automatically)
- A color scale is used for numerical columns

fig = px.bar(data_frame=student_scores, 
      x="student_name", 
      y="score", 
      title="Student Scores by Student"
      color="city")
fig.show()

Our colors revealed

The plot before:

Bar chart without colors

Our plot after:

Bar chart with colors

Color with univariate plots

Using plotly.express color argument with univariate (bar, histogram) plots:

Histograms - stacked bars
Box plots - produces multiple plots

Stacked histogram with color

side by side boxplot with color

Specific colors in plotly.express

color_discrete_map: A dictionary that maps categorical values to colors
Can also express (basic) colors as strings such as "red", "green" etc.

Our specific colors

fig = px.bar(
    data_frame=student_scores, 
    x="student_name", y="score", 
    title="Student Scores by Student",

    color_discrete_map={
    "Melbourne": "rgb(0,0,128)",
    "Sydney": "rgb(235, 207, 52)"},

    color="city")

Bar chart with specified colors

Color scales in plotly.express

Single color scales (light to dark green)

Green color scale

Blended gradient (green into blue)

color_continuous_scale argument for color scales.

Green blue color scale

Using built-in color scales

fig = px.bar(data_frame=weekly_temps, 
    x="day", y="temp", 
    color="temp",
    color_continuous_scale="inferno")
fig.show()

Many built-in scales available

Bar chart with inferno colorscale

Constructing our own color range

Custom color scale (yellow - orange - red)

my_scale=[("rgb(242, 238, 10)"),
          ("rgb(242, 95, 10)"), 
          ("rgb(255,0,0)")]

fig = px.bar(data_frame=weekly_temps, 
    x="day", y="temp",

    color_continuous_scale=my_scale,
    color="temp")

Bar char our own color scale

Let's practice!

Introduction to Data Visualization with Plotly in Python