I'm pretty certain I could tell the difference between a cold and hot blue instantly.. It's not just the colour, but the polish job.. personally I don't Have The tools or skills to do a 'restoration', but , same as you, I have breathed life back into plenty of guns that hopefully will shoot for another 30 or 40 years before needing attention again.
I would say that anyone saying they have 'restored' a gun is being dishonest UNLESS that gun looks like it has been wrapped in an oily rag since manufacture..