Set color map for bar plot while using the `color` encoding channel

Question

In the below example, I create an bar plot, with the height and the color of the bars both encoding the y column of df. The bars then appear in different shades, for very light to very dark; in blue.

import altair as alt
import numpy as np
import polars as pl


N = 20
df = pl.DataFrame({
    'x': range(N),
    'y': np.random.randint(0, 100, N)
})
alt.Chart(df).mark_bar().encode(x='x', y='y', color='y')

Now, how do tell altair to use the same encoding but apply another color map of my liking, such that the bars are displayed in, e.g. shades of yellow?

Adding color=yellow to mark_bar does not work, as it is overwritten by the subsequent encoding.

Shivam Bhosle · Accepted Answer · 2025-07-10 10:42:00Z

'yellow' is not a valid color scheme in Altair. The valid color schemes listed include options like 'yellowgreen', 'yelloworangered', and 'yelloworangebrown', but not 'yellow'

Check here: https://vega.github.io/vega/docs/schemes/

Corrected Code:

import altair as alt
import polars as pl
import numpy as np

N = 20
df = pl.DataFrame({
    'x': range(N),
    'y': np.random.randint(0, 100, N)
})

alt.Chart(df).mark_bar().encode(
    x='x',
    y='y',
    color=alt.Color('y', scale=alt.Scale(scheme='yelloworangered'))
)

If you want a more specific yellow gradient, you can define a custom range:

alt.Chart(df).mark_bar().encode(
    x='x',
    y='y',
    color=alt.Color('y', scale=alt.Scale(range=['#FFFFE0', '#FFC107', '#FFA000']))
)

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