Changing color in cell based on contents

Just inherited a ss and cannot figure out how a cell changes color based on its contents.

Basically, the cell has a formula that evaluates to a "R", "G" or "Y", and is then changed into Red, Green or Yellow based on its value. However, I cannot find the actual function/procedure that runs to change the color of the cell. I have unprotected the ss, and unhidden all the hidden worksheets to no avail. The only SUB I see is under Module 1 called turnred:
Sub turnred()
'
' turnred Macro
' Macro recorded 3/24/99 by Karl Barthel
'

'
Selection.Interior.ColorIndex = 3
End Sub

but I cannot find a call to it in any of the sheets. And besides, this sub only handles red, not green and yellow.

What am I missing? What are the other possible ways to change color in a cell based on its value other than a sheet-level macro? Or how else can you hide a macro within a sheet?

Thanks