[V8i VBA] How to determine a form control's object name?

Bit of a generic VBA question but I've yet to discover the answer I'm looking for.

• I have a form with 3 textbox's for RGB input values (TB_CustomRed, TB_CustomGreen and TB_CustomBlue).
• I have the following function which validates that the values entered are only numbers and have a max value of 255:

Private Sub ValidateRGB()
    Dim lRGB_Max                             As Long

    lRGB_Max = 255
    With Me.Controls("TB_CustomRed")
        If Not IsNumeric(.Value) And .Value <> vbNullString Then
            MsgBox "Sorry, only numbers allowed"
        ElseIf Val(.Value) > lRGB_Max Then
            MsgBox "Enter a number between 0 and 255"
        End If
    End With
End Sub

I call the subroutine in the change event handler like so:

Private Sub TB_CustomRed_Change()
    ValidateRGB
End Sub

Private Sub TB_CustomGreen_Change()
    ValidateRGB
End Sub

Private Sub TB_CustomBlue_Change()
    ValidateRGB
End Sub

The problem is I have hard-coded the textbox object name at the start of the With statement (obviously it will have no effect for the green and blue text box's) and to avoid duplicating the sub a further 2 times ( or manually writing the control objects name in its change event) I want to instead pass the name of the object as an argument to ValidateRGB however I am unsure I determine the name of the object. Some search results advise to use Screen.ActiveControl.Name however I think that's either part of the office products object libraries or only works within the IDE of those applications so I'm looking for an alternative.