This study examined the color and spot patterns for the ventral petals of a cross line in Sinningia speciosa. The second generation individuals of the cross line exhibited phenotypic segregation in floral color and spot patterns. Three color traits (color region ratio, region of interest color, and color gradient) and five spot traits (spot quantity, spot density, spot area ratio, spot color, and background color) were defined and quantified using image processing techniques. The variation in the traits and the correlations between the traits were also investigated. The results indicated a considerable degree of variation among the traits. The proposed approach can quantify petal traits more objectively and precisely compared with conventional naked examination. Thus, it can be used for applications, such as new flower variety determination, that require precise trait quantification.