Checklist

• I have searched the existing issues for similar issues.
• I added a very descriptive title to this issue.
• I have provided sufficient information below to help reproduce this issue.

Summary

In a multi-line plot, st.line_chart() always re-orders the columns in data, presumably in alphanumeric order. This leads to wrong assignments of color and column names appear in the legend in wrong order.

Reproducible Code Example

# line_chart_bug.py
import streamlit as st

chart_data = {'c_one': [1, 1, 1], 'b_two': [2, 2, 2], 'a_three': [3, 3, 3]}
st.line_chart(
    chart_data, 
    y=['c_one', 'b_two', 'a_three'], 
    color=[(255, 0, 0), (0, 255, 0), (0, 0, 255)]
)

Steps To Reproduce

$ streamlit run line_chart_bug.py

Expected Behavior

kwarg y should determine the order of columns in the plot and when omitted/None, columns should be plotted in the same order as the column index.

Current Behavior

• Legend shows columns in wrong order: "a_three", ... which depends entirely on column names, not the order of the sequence y
• Colors in color are assigned to the wrong lines: "c_one" should be red not blue.

Is this a regression?

• Yes, this used to work in a previous version.

Debug info

• Streamlit version: 1.39 ... 1.47.1 (all tested)
• pandas 2.2.3
• Python version: 3.12.7
• Operating System: ubuntu 24.04
• Browser: chrome-based

Additional Information

Temporary workaround: you can modify the column order by prepending column names with spaces.