You can use Select Case to act on multiple options at the same time. For example if you want to treat turquoise, pink AND mixed in the same way...
Code:
Sub ClearHilites()
Dim oRngStory As Range
For Each oRngStory In ActiveDocument.StoryRanges
With oRngStory.Find
.Highlight = True
Do While .Execute
Select Case oRngStory.HighlightColorIndex
Case wdTurquoise, wdPink, 9999999
oRngStory.HighlightColorIndex = wdNoHighlight
oRngStory.Collapse 0
End Select
Loop
End With
Next
End Sub