I have been using whitening strips recently but just notices that i have a small green blob in the centre of my molar. any ideas of what this is?

Green blob?: Nothing comes to mind if the color is really green. Perhaps it's a stained filling or decay under the surface of the tooth. See a dentist to determine what it is and what can be done about removing it.

Have evaluation: Could be an old filling or sealant that needs replacement. Ask your dentist to have a look.

green: The color could mean microleakage of some sort, whether there was a sealant, a resin or whatever was placed, more likely no longer sealed, so need to see your dentist to get it checked out.