The concentration of major anthocyanins, quercetins, catechin, and phenolic acids during flower development of Rosa ×hybrida L. ‘KORcrisett’ was quantified using high-performance liquid chromatography/mass spectrometry. Additionally, the changes in petal color were monitored colorimetrically at four different stages of development (bud, partially open flowers, fully open flowers, senescent flowers) and correlation was calculated between the chromaticity parameters and major/total anthocyanins. Color parameters a*, b*, and h° decreased with the progression of flower development and a*/b* ratio and lightness (L*) increased. In rose petals, a negative trend in the content of major (pelargonidin-3,5-di-O-glucoside, cyanidin-3,5-di-O-glucoside) and minor (pelargonidin-3-O-glucoside, cyanidin-3-O-glucoside, peonidin-3-O-glucoside) anthocyanins was observed during flower development. Buds contained almost threefold higher concentrations of pelargonidin-3,5-di-O-glucoside and fourfold higher concentrations of cyanidin-3,5-di-O-glucoside than senescent flowers. Buds also contained significantly more quercetins (quercetin-3-O-rutinoside, quercetin-3-O-glucoside, and quercetin-3-O-rhamnoside), catechin, and phenolic acids (gallic acid, protocatechulic acid, chlorogenic acid, caffeic acid, p-coumaric acid) than flowers of subsequent developmental stages. The most significant differences were observed in the content of gallic acid; buds contained almost sixfold higher values than senescent flowers. Correlation analysis revealed a strong correlation between chromaticity parameters a*, b*, a*/b* ratio, h°, L*, and major/total anthocyanins with values ranging from 0.60 to –0.84.