A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
SumColor is not a builtin Excel Function.
It is a UDF ( User Defined Function)
See Chip Pearson's site for more on SumColor
http://www.cpearson.com/excel/colors.aspx
Probably resides in your Personal Macro Workbook
Might be it did not get loaded for some reason when Excel started.
Do a search for that file. . . . . .Personal.xlsb or .xlsm
Generally located in XLSTART folder.
Gord