So, this would basically be a new pattern color with two possible outcomes: if a nicheling has only one copy of the gene, then their pattern glows in the other color present, and is purely aesthetic. If a nicheling has two copies of the gene, then it would glow in a random, bright color (like toxic body). Maybe having two copies would add +1 attractiveness out of water, and in water fish would come toward the bioluminescent nicheling.