To get club foreground and background colour working as intended, change line 5 in "clubforegroundcolor.txt" and "clubbackgroundcolor.txt" to
echo ^<colour id="new_value" variable/^>
both files are located in D:\...\FM23 Editor Generator ver 1.0\FM23 Editor Generator ver 1.0\System
Likewise, you need to have the year founded column ahead of the colours in the text file used to generate the .xml, and have the colours written like @griffin99's example above (red="255" green="255" blue="255" alpha="255").
EDIT:
to save the reader a few moments, this works in Excel (obviously change the column numbers to the ones you have the RGB values in).
=CONCAT("red=",CHAR(34),I3,CHAR(34)," green=",CHAR(34),J3,CHAR(34)," blue=",CHAR(34),K3,CHAR(34)," alpha=",CHAR(34),255,CHAR(34))