<p>The armament–ornament model suggests that females may benefit from exploiting signals that indicate status or are used in male-male aggressive interactions as such traits may impose costs. Here, we investigated whether the blue belly patches displayed by mesquite male lizards, <i>Sceloporus grammicus</i>, are used during male-male and female-male interactions. In the first experiment, males interacted with another male of similar size whose blue belly patches were manipulated to appear dull or bright, or remained unmanipulated. In the second experiment, females observed two males paired by size featuring either unmanipulated, dull, or bright blue belly patches. We found that males were less aggressive toward males with brighter and bluer patches, and females displayed more behaviors toward brighter males than toward males with unmanipulated blue patches, although it remains unclear whether females courted or rejected these males. Our results suggest that the ventral blue belly patches have a dual function in mesquite lizards, influencing antagonistic interactions among males and interactions between females and males.</p>