EDIT: here is working code to do exactly what you asked, i'm sure alot of people will find it crude but hey i'm entirely self taught and it works so who cares?
Sub Macro1()
On Error Resume Next
Dim current As String
For i = 1 To 65536 ' go from first cell to last
current = "c" & i ' cell counter
Range(current).Select ' visit the current cell
If Range(current).Text = "add" Then ' if it says add then we...
With Selection.Interior
.ColorIndex = 3 ' ...go red
.Pattern = xlSolid
.PatternColorIndex = xlAutomatic
End With
End If
If Range(current).Text = "remove" Then ' if it says remove then we...
With Selection.Interior
.ColorIndex = 4 ' ...go green
.Pattern = xlSolid
.PatternColorIndex = xlAutomatic
End With
End If
Next i ' loop and check the next cell
End Sub
you could obviously build in extra 'if' statements for all kinds of stuff, or extra code to do more stuff with the cells containing the words you're looking for but the above covers what you were asking for - macro code to change cell colours depending on their contents.
although the code i wrote for you above works well, i personally think that the post above is a much crisper way of doing things because it doesn't rely on the user having macros enabled and having to run a macro.
but if it *was* a macro you were after then i hope this helped, and is worthy of the 10 points for best answer ;)