Insight-HXMT CCD of 4U 1636–536, where soft-color is defined as the ratio of LE 3–6 keV to 1–3 keV count rates, and hard-color is defined as the ratio of ME 15–20 keV to 10–15 keV count rates. Correction is made by dividing by the count rate of the Crab corresponding to the time and energy band. The time bin of the points is 4 h. The stars are the type I bursts used in the paper. The average error bar is shown in the top right corner. The color bar shows the levels of significance of hard X-ray shortage during the bursts. The bursts in the hard state are classified into four groups based on their positions on the CCD.