This function is an example. Note that the RGB values are actually BGR values. Why does excel do this?
Function GetRGB(ByVal cell As Range) As String
Dim R As String, G As String
Dim b As String, hexColor As String
hexCode = Hex(cell.Interior.Color)
'Note the order excel uses for hex is BGR.
b = Val("&H" & Mid(hexCode, 1, 2))
G = Val("&H" & Mid(hexCode, 3, 2))
R = Val("&H" & Mid(hexCode, 5, 2))
GetRGB = R & ":" & G & ":" & b
End Function