How animals assess information encoded in individual colour patches have been extensively studied, yet the role of both individual colour patches and gross colour pattern (i.e. the combination of colour patches) remains understudied. We tested the functioning of both individual colour patches and gross colour pattern in sexual selection using the jumping spider Siler semiglaucus as a study system. We first quantified sexual dimorphism in S. semiglaucus in both individual patches and gross colour pattern using the newly developed quantitative colour pattern analysis (QCPA) framework. After detecting sexual differences in colour coverage and pattern contrast, we manipulated the abdomen colour pattern of males and had them engage in both female mate choice and male contest trials. Females spent more time watching males with lower pattern contrast and greater red coverage during mate assessment, suggesting that they evaluate information from both individual patches and gross colour pattern of males. However, male colour pattern had no significant effect on the outcomes of male contests. Thus, we suggest that the observed sexual colour pattern dimorphism evolved primarily through female mate choice in S. semiglaucus. This is the first study to use QCPA framework to quantify sexual dimorphism in within-pattern conspicuousness from an intraspecific perspective in invertebrates. Our study also highlights the importance of both individual colour patches and gross colour pattern in sexual selection.