import openpyxl as px
from openpyxl.styles import PatternFill

filepath = r'c:\sample/excel_test/test.xlsx'
savepath = r'c:\sample/excel_test/test2.xlsx'
wb = px.load_workbook(filepath)
ws = wb.get_sheet_by_name('Sheet1')

ws.cell(row = 3, column = 3).fill = PatternFill(patternType='solid', fgColor='ffc040')

wb.save(savepath)
 

AD