For all three visual systems, blue categories (UV/Blue, Blue/Red, and Blue) were the most contrasting colors against an average coral background (t > 2.14, p < 0.05; Figure 3). UV/Blue and Blue/Red were significantly more contrasting than an average of the ten noncleaner colors combined (UV/Blue t = 4.07, p < 0.001; Blue/Red t = 10.12, p < 0.001; Figure 3). Therefore, a blue coloration, irrespective of color category, appears to be one of the most conspicuous colors when signaling to a variety of signal receivers against a coral reef background.