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Ornamental kale is a popular decorative plant. We identified a peculiar bicolor leaf double haploid line, with green margins and red centers. The development of bicolor leaves can be divided into three stages: S1, S2, and S3. To probe the reason for bicolor formation, we analyzed the anthocyanin and chlorophyll contents, detected the changes in indole-3-acetic acid (IAA), abscisic acid (ABA), gibberellin 3 (GA3), sugar, and starch contents, and identified the differentially expressed genes (DEGs) using RNA-seq. Results showed that the bicolor leaf phenotype is gradually formed with anthocyanin degrading and chlorophyll accumulation. Anthocyanin content is lower in the green margin (S3_S) than in the red center (S3_C) part at S3. IAA content was positively correlated with anthocyanin content during the bicolor leaf development. During anthocyanin degrading from S1 to S2, <i>cinnamate-4-hydroxylase</i> (<i>C4H</i>) and <i>transport inhibitor response 1</i> (<i>TIR1</i>) were downregulated, while <i>lateral organ boundaries domain 39</i> (<i>LBD39</i>) was upregulated. Two peroxidases, two &#946;-glucosidases (<i>BGLU</i>), <i>LBD39</i>, <i>LBD37</i>, <i>detoxifying efflux carrier 35</i> (<i>DTX35</i>), three <i>no apical meristem</i> (<i>NAC</i>) transcription factors (TFs), and 15 WRKY DNA-binding protein (WRKY) TFs were downregulated in S3_S <i>vs.</i> S3_C. The bicolor phenotype was mainly linked to anthocyanin degrading and chlorophyll accumulation, and that anthocyanin degrading resulted from reduced anthocyanin biosynthesis and increased anthocyanin degradation.