What is the value of a 1957 US 1 dollar silver certificate with a blue seal?

Answer 1

1957 was the last series year issued before silver certificates were discontinued so many of them were saved as keepsakes. Because of that most 1957 $1 bills are only worth about $1.50 or so in average condition. If it's crisp and uncirculated, it might sell for around $2 if there's no letter next to the date, or $3 if there's an A or B.

Why blue?

Blue seals were used on all silver certificates issued from 1928 to 1957.

Serial Numbers

A bill's serial number is just a counter so including it in a question generally doesn't help to identify it or affect its value. There are collectors who will pay a premium for bills with low or patterned serial numbers; e.g.12345678 or 00000005.

Silver Value

It's no longer possible to redeem silver certificates for silver metal. That practice was ended after the price of silver was deregulated, to prevent people from "gaming" the exchange process by trading bills for metal and vice versa as rates fluctuated.

Silver Certificates were abolished by Congress on June 4, 1963 and all redemption in silver ceased on June 24, 1968. However the bills have never been withdrawn or demonetized so they're still valid legal tender.