Setting up Customer ID as Primary Key

For that you'd use the NotInList event procedure of the ColorID combo box in the subform to insert a row into the Color table:

Private Sub ColorID_NotInList(NewData As String, Response As Integer)

    Dim ctrl As Control

    Dim strSQL As String, strMessage As String

    Set ctrl = Me.ActiveControl

    strMessage = "Add " & NewData & " to list?"

    strSQL = "INSERT INTO Color(Color) VALUES(""" & _

            NewData & """)"

    If MsgBox(strMessage, vbYesNo + vbQuestion) = vbYes Then

        CurrentDb.Execute strSQL, dbFailOnError

        Response = acDataErrAdded

    Else

        Response = acDataErrContinue

        ctrl.Undo

    End If

End Sub

When the user types a new colour into the combo box they'll be prompted to confirm the addition of the new item to the list, and on their answering yes, the code executes an SQL statement to insert a row into the table.

Worked perfectly as well.

Is there a way to make it so that certain fields can't be modified unless a field has a specific value?

There is a Yes/No column in my table and if the answer is "Yes", I would like only certain fields to be modified so the user can enter data.  However, if "No" is selected, I would like a different set of fields to be modified for data entry so certain fields should remain grayed out. Also, there are a few "Other" options in some of my lists so if "Other" is selected, I would like the user to be able to input data into a text field next to it, otherwise it should remained grayed out.

For future reference, when introducing a new topic, please start a new thread rather than tacking it on to an existing one.

You need to do this in two places, so to avoid duplication of the code put it in a function in the form's module.  Assuming you have a check box as the control for the Boolean column:

Private Function EnableControls()

   ' set check box to False by default

   Me.[YourCheckBox].DefaultValue = """" & False & """"

   ' enable one set of controls if Boolean column is True

   Me.SomeControl.Enabled = Me.[YourCheckBox]

   Me.SomeOtherControl.Enabled = Me.[YourCheckBox]

   ' etc

   ' enable another set of controls if Boolean column is False

   Me.AnotherControl.Enabled = Not Me.[YourCheckBox]

   Me.YetAnotherControl.Enabled = Not Me.[YourCheckBox]

   ' etc

End Function

You can then call the function as both the form's On Current event property and as the AfterUpdate event property of the check box with:

    =EnableControls()

However, there is one fly in the ointment.  If the user checks the check box, but then undoes the record with the Esc key the controls will remain enabled/disabled, the opposite of what they should be.  Checking and unchecking the check box will return the properties to their correct values, but this is not satisfactory.  One would imagine the form's Undo event procedure might be the answer, but this executes before the record is undone, so doesn't help.  At present I don't know any way of solving this, but will post a thread later to see if anyone else has a solution.

Okay, I will make a new topic in the future. Thanks for your assistance with all of that. I am currently applying everything I have learned here to the actual database. Everything seems to be working as intended so far and it looks much better than before.

I'm still working on the feature to enable some controls and disables others based on either a Yes/No or "Other" selection in a Combo List. It would be ideal to have this feature, but it isn't crucial right now.

I have one question pertaining to a topic discussed earlier in the thread about the junction tables and subforms. If a user selects a Color by accident and tries to remove the color, it brings up the error message saying "You must enter a value in the [name] field." I have AllowEdits and AllowDeletions enabled on the Main form and Subform, but I can't find any option to delete the entry either by right clicking the combo box or the right clicking the record selector. I can hit "Delete Record" through the Home ribbon and remove the record, but nothing within the form itself. 

Is there anyway to remove a record through the subform or form itself? Maybe if it detects a blank value, then don't save the record or delete it? 

Would something like the below work?

If

Me.cboColor = ""

Then [delete record]

You must either undo the incorrect colour selection by pressing the Esc key before saving the subform record, or if the record has been saved, delete the record by clicking on the record selector to select it and then pressing the Delete key.