The paint shop suppliers have the paint codes for all makes of cars, for all models, and all years, pretty much since the beginning of cars. You tell them you would like a one stage paint for a 1956 Ford Thunderbird in peacock blue.
Go online and search for peacock blue TBirds at Amos Minter, or such sites. Print off a colour photo. Or contact Amos Minter.com and ask their restoration staff for the paint code they use. The cars they turn out are correct in all aspects, so the colours they use will be original. Good Luck!