Openpyxl: Decode 'auto' color to rgb value

Question

I am trying to determine the color of borders set in an Excel document. I use the 'openpyxl' library (latest Version 3.0.9) and encountered a problem to extract the rgb color code when the user sets the border via the default 'auto' color.

When I extract the cell color property, I see this (in my debugger, see screenshot). None of the cell fields are set with an RGB code, the fields indicate some problem with extracting the color information. I assume this is due to the 'auto' color.

The index color probably refers to this in documentation:

Default Color Index as per 18.8.27 of ECMA Part 4

COLOR_INDEX = (
    '00000000', '00FFFFFF', '00FF0000', '0000FF00', '000000FF', #0-4
    '00FFFF00', '00FF00FF', '0000FFFF', '00000000', '00FFFFFF', #5-9
    '00FF0000', '0000FF00', '000000FF', '00FFFF00', '00FF00FF', #10-14
    '0000FFFF', '00800000', '00008000', '00000080', '00808000', #15-19
    '00800080', '00008080', '00C0C0C0', '00808080', '009999FF', #20-24
    '00993366', '00FFFFCC', '00CCFFFF', '00660066', '00FF8080', #25-29
    '000066CC', '00CCCCFF', '00000080', '00FF00FF', '00FFFF00', #30-34
    '0000FFFF', '00800080', '00800000', '00008080', '000000FF', #35-39
    '0000CCFF', '00CCFFFF', '00CCFFCC', '00FFFF99', '0099CCFF', #40-44
    '00FF99CC', '00CC99FF', '00FFCC99', '003366FF', '0033CCCC', #45-49
    '0099CC00', '00FFCC00', '00FF9900', '00FF6600', '00666699', #50-54
    '00969696', '00003366', '00339966', '00003300', '00333300', #55-59
    '00993300', '00993366', '00333399', '00333333',  #60-63
)
# indices 64 and 65 are reserved for the system foreground and background colours respectively

The documentation says that Index 64 is reserved so there is no point in trying to access the color array (max index is 63).

Source: https://openpyxl.readthedocs.io/en/stable/_modules/openpyxl/styles/colors.html

I can be brave and deal with index 64 as black, which seems to be the eternal auto-color anyway but I am wondering if there is a proper way to decode the 'auto' color from Excel?

Answer 1

System colours are set by the application. Windows defaults will be white background and black foreground. You can check the colors part of the styles.xml to see if these have been overriden, but really the client application gets to decide.