Will Lidocaine/Prilocaine 2.5% blanch my skin?

First -- 2.5% lidocaine is not strong enough to numb your skin, so it will not help you anyway.
Second -- most topical lidocaine will redden the skin, making the IPL target more areas than just the dilated vessels, so this would make the treatment less successful (and probably more painful)
Third -- Lidocaine with epinephrine will blanch the skin -- so perhaps that's what they are referring to -- but this is only in injectible lidocaine, not in topicals.
People have very variable levels of pain with IPL-- some feel it is painful but many do not. Make sure you tell the person doing it that you have a low pain tolerance, and they can start at a lower setting and work up from there. Good luck!

Thank you for your question FaceMe21. I understand your concern.
IPL is a great treatment for facial rejuvenation. It works well for redness. We apply topical numbing cream prior to a treatment and still get great results. Some people take niacin before a treatment. This brings blood to the skin to increase the target. We have not found this necessary. Please consult with a doctor for specific recommendations. Good luck!

Products like EMLA with Lidocaine and Prilocaine cause vasoconstriction of small blood vessels in your skin.  This makes the skin look lighter for a few hours, but does not permanently lighten your skin color.