Signal-to-noise for candidate food dyes in Con-Ex. Data are the summed absorbance values of INT + ExVial. Dye (simple filled bars): absorbance values from flies fed media containing 1% of the indicated dyes (signal). No Dye (hatched bars): absorbance values from flies fed media without dye (noise). Control r[A] female flies (20/vial) consumed media and excreted waste products in vials for 24 h. Numbers in brackets indicate signal-to-noise ratios. Signal (Dye) was greater than noise (No dye) in experiments with (panel A) Blue 1, xylene cyanol (XC) and Red 40, and (panel B) Blue 2, Red 4 and Yellow 5 (*individual two-tailed t tests, p = 0.007 to <0.0001, n = 5–6).