Help with Schwinn le tour identification

[JayTheDiver]

I recently inherited a Schwinn Le Tour from my ex mother in law. The serial number is B737882. It is located on the crank tube. The color is an off-white. From my research the serial for a 1977 should be BNXXXXXX not B737XXX. And I don't see that color as an option in any years. Any help greatly appreciated.
Jason