Add the Notes field as a small hidden control.
Create a separate popup form to display the Notes.
On the main form, add this to the form current event
Code:
if Me.Notes<>"" Then
. Me.mybuttonName.Picture= ..... enter full path to greenmemo.jpg here
Else
...similar code for redmemo.jpg
End if
The button itself click code would open your popup form.
However a better method is to enable / Disable the button
Code:
if me.notes<>"" then
. Me.buttonnwme.enabled=true
Else
. Me.buttonname.enabled=false
End If