Although Bix wasn't a "blues" player as such, he often employed what are sometimes termed "blue" notes in his solos, i.e. flattened 3rds and flattened 7ths, and sometimes flattened 5ths. He would also sometimes bend other notes, landing on them perfectly in tune and then slightly altering the pitch (as he held the note) for effect. Many white jazz musicians did this and it doesn't necessarily make them "blues" players either! But Bix's deep appreciation of black jazz musicians and blues singers is well known, and one only needs to think of Louis Armstrong and Ethel Waters in this respect.
One always associates these so-called blue notes with Bix's cornet playing rather than his piano playing. As is well known, his piano playing was highly influenced by the European school of classical music and the impressionist composers in particular. Therefore, it is interesting to read that he occasionally played "the blues" on piano. The following comment comes from drummer Virgil Leech. Leech was a member of Jimmie Caldwell's band, composed of students at Northwestern University, including Don Murray. Bix was guest cornettist with the band when they played for the Senn High School Prom at the Edgewater Beach Hotel in Chicago on Thursday, January 26th, 1922:-
"Bix came down early the next afternoon [Northwestern campus] to run over a few difficult pieces in which Caldwell wanted him to play a "break". We had to go out and find him a clean shirt. Besides being the greatest on cornet, he could play what we termed a "negro piano". Playing the blues, he was terrific!"
Virgil Leech, letter to Philip Evans, 7/7/1973, quoted in "Bix: The Leon Bix Beiderbecke Story" by Philip R. and Linda K. Evans.