Methane-sensitive photometric diagnostics for the controlled methane-abundance sweep. Left: planet F877–F661 color versus F729–F661 color. Right: planet F877–F661 color versus apparent F729 AB magnitude. Symmetric error bars indicate measurements derived from detected bands, while open symbols with arrows denote one-sided limits when F877 is below the adopted detection threshold. The gray curves show the theoretical loci as the methane scaling factor changes.