Flower color is one of the most important ornamental traits of tulips (Tulipa gesneriana). Five typical tulip cultivars were selected to identify the flavonoid components and analyze their key gene expression in their tepals. Firstly, after preliminary determination of the pigment type, the flavonoids were identified by UPLC-Q-TOF-MS. A total of 17 anthoxanthins were detected in the five cultivars. The total anthoxanthin content in the white tulip and the red tulip showed a similar decreasing trend, while an increasing trend was observed in the black tulip. Similarly, a total of 13 anthocyanins were detected in five tulip cultivars. The black tulip contained the largest number of anthocyanins, mainly delphinidin derivatives (Dp) and cyanidin derivatives (Cy). The total anthocyanin content (TAC) in the orange, red, and black cultivars was higher than that in the white and yellow cultivars and presented an overall increase trend along with the flower development. TgCHS, TgFLS, TgF3H, TgF3′H, TgF3′5′H, and TgDFR, as key structural genes, were involved in the flavonoid synthesis pathway, and the expression patterns of these genes are basically consistent with the components and accumulation patterns of flavonoids mentioned above. Taken together, the flower color in tulips was closely related to the composition and content of anthocyanins and anthoxanthins, which were indeed regulated by certain key structural genes in the flavonoid pathway.