It wasn't apparent from what you had previously posted that you wanted the entire page to change colour, and not just the text. For that, you could use:
Code:
Sub Colorize()
With ActiveDocument
.Background.Fill.Visible = msoTrue
Select Case .Range.Font.ColorIndex
Case wdAuto, wdBlack
.Range.Font.ColorIndex = wdWhite
.Background.Fill.BackColor.TintAndShade = wdBlack
Case wdWhite
.Range.Font.ColorIndex = wdYellow
.Background.Fill.BackColor.TintAndShade = wdBlack
Case wdYellow
.Range.Font.ColorIndex = wdAuto
.Background.Fill.BackColor.TintAndShade = wdNoHighlight
.Background.Fill.Visible = msoFalse
End Select
End With
End Sub