Differential expression of shared genes in back feathers between control unornamented (UN) and ornamented (OR) males (x-axis) and between unornamented and testosterone-implanted (TI) males (y-axis); genes that are significantly overexpressed (adjusted P < 0.1) in red feathers (in both ornamented males and testosterone-implanted males) are located in the top right quadrant, and genes that are significantly overexpressed in brown feathers (unornamented males) are in the bottom left quadrant. Significantly differentially expressed genes are colored and labeled in red.