Summary In Brassica napus , yellow petals had a much higher content of carotenoids than white petals present in a small number of lines, with violaxanthin identified as the major carotenoid compound in yellow petals of rapeseed lines. Using positional cloning we identified a carotenoid cleavage dioxygenase 4 gene, BnaC3 . CCD 4 , responsible for the formation of flower colour, with preferential expression in petals of white‐flowered B. napus lines. Insertion of a CACTA ‐like transposable element 1 ( TE 1) into the coding region of BnaC3 . CCD 4 had disrupted its expression in yellow‐flowered rapeseed lines. α‐Ionone was identified as the major volatile apocarotenoid released from white petals but not from yellow petals. We speculate that BnaC3. CCD 4 may use δ‐ and/or α‐carotene as substrates. Four variations, including two CACTA ‐like TE s (alleles M1 and M4) and two insertion/deletions ( INDEL s, alleles M2 and M3), were identified in yellow‐flowered Brassica oleracea lines. The two CACTA ‐like TE s were also identified in the coding region of BcaC3 . CCD 4 in Brassica carinata . However, the two INDEL s were not detected in B. napus and B. carinata . We demonstrate that the insertions of TE s in BolC3 . CCD 4 predated the formation of the two allotetraploids.