Public Sub AlertMe()
Dim condition As Range
Dim alert_this As Worksheet
Set condition = Worksheets("Sheet1").Range("A1")
Set alert_this = Worksheets("Sheet2")
'NOTE: .Value must be compared based on the type of data in the cell.
'CAVEAT... Since VBA True/False is really -1/0, the only reliable
'compare is <> False, unless you use -1 to indicate True.
If condition.Value <> False Then
'index colors are found in PatternColorIndex docs.
'or .Color = RGB(x,x,x) instead of ColorIndex.
alert_this.Tab.ColorIndex = 5
Else
'ColorIndex is simplest to get "default" colorization.
alert_this.Tab.ColorIndex = xlColorIndexNone
End If
End Sub