The effect of shading in midsummer on anthocyanin and non-flavonoid polyphenol biosynthesis of Gynura bicolor DC leaves was examined using a control (full solar radiation) and a shade treatment (50% shading of full solar radiation). Leaf temperature in the shade plot remained ≈40 °C in the daytime, ≈6 °C lower than in the control. Plants in the shade plot grew better than the control. The content of chlorogenic acid (CGA) in leaves decreased with leaf maturation for both treatments, and a larger amount of CGA was detected in leaves from the control than the shade treatment. The profiles of reactive oxygen species (ROS) scavenging activity exhibited an identical pattern to the content of CGA. Although there was an abrupt increase in the content of anthocyanin in the early stage of leaf expansion, the content decreased rapidly as the leaves matured. The increase in anthocyanin early during leaf expansion was much more limited in control leaves than shaded leaves. There were no correlation between the profiles of anthocyanin and gene expression such as GbPAL, GbC4H, Gb4CL, GbCHS, GbCHI, GbF3H, and GbUFGT. However, the profiles of expression of genes such as GbMYB2, GbF3′H, GbDFR, and GbANS were similar to the anthocyanin profiles. These results suggest that artificial shading in midsummer is an effective method to promote anthocyanin accumulation but reduces ROS scavenging capacity as a result of lowered CGA production.