In 1969, Katsuyoshi Inokuma graduated from a high school in Fukushima Prefecture. After studying art at an art academy and an art institute, he returned to his hometown in 1972. In 1966, he was awarded the Grand Prize at the Memorial of AOKI Nishinippon Art Exhibition, which led him to pursue a full-time career as an artist.
During the 1990s, Inokuma began creating abstract paintings dominated by shades of blue. In 1993, he introduced his ongoing series called IN BLUE, characterised by gentle and soft blue partitions with dotted rectangular shapes. In his recent works, Inokuma has departed from his earlier decorative expression, which incorporated vibrant colours and dripping techniques within the IN BLUE series. Instead, he explores serene white and black tones, creating a sense of depth in the artwork. In addition, he covers his paintings entirely in his signature ultramarine blue, known as 'Inokuma Blue.' Certain sections of the paintings are built up with multiple layers of paint, enhancing the depth and complexity of the artwork. To enrich the depth of the blue colour, Inokuma incorporates a pink underpainting. Additionally, he adds coffee grounds to specific areas of the underpainting, creating a random and uneven texture that reflects light and produces intricate colour surfaces.