Identifying which phone number an SMS was sent from

Hi,

I have a contact with multiple phone numbers. When she sends me an SMS, I'd like to know from which number she's sending it. I know I can go to the "Contact" button at the top of the Messages app, and one of the saved phone numbers for this contact will appear in blue. Is the phone number in blue the number from which the last SMS was sent ? If so, is there any way for me to see from which phone number the previous SMSs were sent ?

Many thanks,

Dustin