Conditional Formatting - Form Based On Text Box Entry

Hello,
Could some kind person out there help me out please?
I have been 'dabbling in' the area of conditional formatting, particularly in the area of changing the colour of my active form based on the result of what’s output on a text box. I have had some success in this area but where I am getting confused is getting the colour of my form to change on the basis of what is entered into a text box control that does not match exactly. My forms background changes to the required colour when its value is ‘set exactly’ but what I am trying to achieve is to change it according to the first letter of entry regardless of what follows? It always starts with a letter, either a ‘D’ or ‘V’ to indicate whether its ‘Vital’ or ‘Desirable’ and is subsequently followed by no more than 6 numbers and finally a letter. Basically I need my form to change colour based on the whether it is either a ‘V’ or a ‘D’ irrespective of what follows???

What I have been using so far is:

Private Sub Model_Number_AfterUpdate()
If Me.Part_Number = "V111145K" Then
Me.Section(acDetail).BackColor = 12632256 'Light Red
Else
Me.Section(acDetail).BackColor = 8421631 'Blah Gray
End If
End Sub


Private Sub Form_Current()
If Me.Part_Number = "V111145K" Then
Me.Section(acDetail).BackColor = 12632256 'Light Red
Else
Me.Section(acDetail).BackColor = 8421631 'Blah Gray
End If
End Sub

Can anyone help me out of a ' sticky situation'..

Ta Very much

Carol