Top-left panel: C_{F275W, F336W, F814W} vs m_F275W − m_F438W pseudo two-colour diagram of the HB stars in NGC 6752. Stars with T < 11 500 K, T > 18 000 K, and 11 500 K < T < 18 000 K are marked with orange, blue, and red points. Top-right panel: m_F275W vs m_F275W − m_F814W CMD of the HB stars in NCG 6752. Bottom-right panel: Histogram of the colour distribution of the photometric data. The purple profile represents the cumulative distribution of the points. The two dashed lines, green and cyan, mark the position of the G- and M- jumps, respectively. Bottom-left panel: m_F438W vs m_F438W − m_F814W CMD of the HB stars in NCG 6752. Where applicable, we plotted the stars in the three ranges of temperature with the same colour coding.