I've never seen that before. Where did you read it. You don't see much blue in the insect world of "trout" food unless they happen upon a New Carner Butterfly. BWO's are a long way from blue. Tied Salmon flies (not the insect of the same name) and steelhead flies abound in various colors. Hope you can remember where you read it. Even hackle with 'blue' in their name are really gray. . Hmmm.