[Python] Inconsistent results with pandas styler applymap

So I am trying to style a pandas dataframe on a streamlit app. I was able to get it to style appropriately with the following code:

df = pd.DataFrame({'A': [1, 2, 3], 'B': [4, 5, 6], 'C': [7, 8, 9], 'X': [10, 11, 12], 'Y': [13, 14, 15], 'Z': [16, 17, 18]})

default_colors = {
"A": "brown",
"B": "blue",
"C": "green",
"X": "orange",
"Y": "red",
"Z": "purple"
}


def highlight_columns(val, color):
return f'color: {color}; font-weight: bold;' if val else ''

if 'A' in df.columns:
styled_df.applymap(lambda val: highlight_columns(val, default_colors['A']), subset=['A'])

if 'B' in df.columns:
styled_df.applymap(lambda val: highlight_columns(val, default_colors['B']), subset=['B'])

if 'C' in df.columns:
styled_df.applymap(lambda val: highlight_columns(val, default_colors['C']), subset=['C'])

if 'X' in df.columns:
styled_df.applymap(lambda val: highlight_columns(val, default_colors['X']), subset=['X'])

if 'Y' in df.columns:
styled_df.applymap(lambda val: highlight_columns(val, default_colors['Y']), subset=['Y'])

if 'Z' in df.columns:
styled_df.applymap(lambda val: highlight_columns(val, default_colors['Z']), subset=['Z'])


But upon refactoring with:

for column in 'ABCXYZ':
if column in df.columns:
styled_df.applymap(lambda val: highlight_columns(val, default_colors[column]), subset=[column])


All columns iterated over are updated to the the final columns color. In this case column 'Z'. What is going on here? Why do the 6 if statements work fine but the loop doesn't?

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