Pronotal margins and elytral background red to orange; most of pronotum and elytral fasciae dark blackish-bronze with blue-green to golden-green reflections. Ventral side extensively testaceous but with dark pigment on sides of prosternum, on most of lower sternal plates and metacoxal plates, and on the outer margins of middle abdominal ventrites.

Despite its wide range from south-western WA to north-western Victoria, Castiarina distinguenda has been seldom collected in SA. It is apparently known here only from a pair collected in 1984 on flowering mallee in the MU Region, and more recently, from two males trapped by A.M.P. Stolarski in the upper SE Region in spring of 2019.