You can use recursion
Public Sub colCtrlReq(frm As Form)
'' Sets background color for required field -> Tag = *
Dim setColour As String
setColour = RGB(255, 244, 164)
Dim ctl As Control
For Each ctl In frm
If ctl.ControlType = acTextBox Or ctl.ControlType = acComboBox _
Or ctl.ControlType = acListBox Then
If InStr(1, ctl.Tag, "*") <> 0 Then
ctl.BackColor = setColour
End If
ElseIf ctl.ControlType = acSubform Then
colCtrlReq frm(ctl.Name).Form
End If
Next ctl
Set ctl = Nothing
End Sub