From the essay by Phil Patton on the iconic folk artist:
What red was to Titian, yellow to Van Gogh, a high singing blue was to Bill Traylor. The blue of his drinking figures, of his houses, of his abstract constructions is “showcard blue,” “cobalt blue,” the same blue those who grew up in the American South remember from the hand painted signs in the window of the local grocery stores, advertising specials–“yams 15 cents/pound.”

This blue is electric–like the urbanized blues of the electric guitar, its brightness a miracle of modern technology. It is not the faded blue of indigo, weathered and worn–of the overalls in which Traylor had spent most of the eighty four years before he began painting, as a slave and sharecropper. But it is the blue of the musical blues.

…What drew Traylor to blue? The artist Charles Shannon, who discovered Traylor drawing and painting on Monroe Street in Montgomery in 1938, supplied him with that blue paint. But Shannon also provided paints of other colors and papers and brushes to supplement Traylor’s original pencil stub and straight edged stick. Of these, Traylor chose the blue, and the occasional red, keeping his palette lean as the chickens and mules he drew, and resorted to no more elegant painting surfaces than the back sides of shirt card boards and ads for Baby Ruth and Snickers candy. Traylor painted Black Horse on the back of a poster advertising a Negro American League baseball game between the Birmingham Black Barons and Cleveland Bears.