Looping from the start can be bad if you are changing the number of revisions inside your loop. You should start from the back if that is the case. If rejecting the revision is problematic, maybe make sure you aren't revision tracking the font formatting steps.
Code:
Sub ManualRevisions()
Dim iRev As Long
ActiveDocument.TrackRevisions = False
For iRev = ActiveDocument.Revisions.Count To 1 Step -1
With ActiveDocument.Revisions(iRev)
Select Case .Type
Case wdRevisionDelete, wdRevisionCellDeletion '2 & 17
.Range.Font.ColorIndex = wdRed
.Range.Font.Shading.BackgroundPatternColor = RGB(222, 222, 222)
.Reject
End Select
End With
Next iRev
End Sub