The blues is an American form of music with origins in the deep south. Over time the blues became part of the foundation of rock and roll. Blues musicians are as recognized by what they wear as they are by their music. There are some staples that are part of the "blues uniform" but part of the allure of the blues is that you can break the rules to get your point across.
Pictures and movie footage of early blues musicians such as Robert Johnson and a young B.B. King show the musicians had a thing for fine suits. The suits were normally dark, accented by a dark tie, and according to Stillsingingtheblues.com that style is still prominent in blues music today. Over the years a dark suit became the thing to wear if you were playing the blues or taking in a blues show.
In its piece "Short History of Blues," History-of-rock.com said the ladies of blues such as Bessie Smith and Victoria Spivey wore dresses considered stylish at the time.
The fedora and the Panama hat are most identified with the blues. The hat should be dark to match the suit. A Panama hat was made famous by such legendary blues musicians as John Lee Hooker who would sometimes use the broad brim to hide his face. The fedora is captured in many historic photos of blues musicians and was immortalized by the "Saturday Night Live" musical act The Blues Brothers.
A fedora is one of the more popular hats around. Many of the Americana pictures we see of 1950's fathers show them wearing fedora hats. You can also see them in popular 1950's movies on top of such stars as Frank Sinatra and Dean Martin.
Besides the broad-brim, the Panama hat has a concave top. They're usually white with a black band around the base of the top, but in the world of blues they are all black.
If you are looking to complete your blues music clothing ensemble, then you will want to invest in a pair of dark sunglasses. You do not need a name brand pair, and they should not be mirrored sunglasses.
The sunglasses connection to the blues is hard to trace, but it really took off when blues/rock musicians started to become popular. ZZ Top wore sunglasses on stage and off, and a whole generation of blues artists followed suit. "The Blues Brothers" movie from 1980 also saw most of the players old and young in sunglasses.