|Assuming that you are using the basic Red and Orange and not some custom color, this should work. I suggest that you try it in a backup copy of your workbook since it can't easily be undone.|
Note: There appears to be a different ColorIndex number for Orange between Excel 2003 and Excel 2010.
If you are running Excel 2003, use ColorIndex 46 for Orange. For 2010 (and I assume 2007) try 44.
Depending on how big your spreadsheets are this could take a while since it checks every cell in the UsedRange.
'Loop through Sheets
For shtNum = 1 To Sheets.Count
'Determine range of cells used
rngAddress = Sheets(shtNum).UsedRange.Address
'Loop through UsedRange
For Each cel In Sheets(shtNum).Range(rngAddress)
'Check for font color of Red (3) or Orange (44 or 46)
'Change it to Automatic if found
If cel.Font.ColorIndex = 3 Or _
cel.Font.ColorIndex = 46 Then
cel.Font.ColorIndex = xlAutomatic
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