altair_dark.py

# Plotting in dark theme with Altair

import numpy as np
import pandas as pd
import altair as alt

alt.renderers.set_embed_options(theme='dark')

arr = np.concatenate([np.random.randn(100, 2), np.random.randint(0, 5, (100, 1))], axis=1)
df = pd.DataFrame(arr, columns=["X1", "X2", "Y"])

alt.Chart(df).mark_circle().encode(
    x="X1",
    y="X2",
    color=alt.Color("Y:N", scale=alt.Scale(scheme="set2")),  # accent, set2, and set3 are my favorite schemes with dark theme
)

Here's the output