Green protection symbols (=) are displayed for many protections on Airbus aircraft, such as for bank, pitch, and high speed protection. However, there is no such symbol for high AOA protection. Rather, there are amber and red strips. Why does only this protection use a different symbol, and moreover, why isn't the same concept applied to high speed protection (no protection symbol), when both change significantly with attitude, configuration, and more? In short, why isn't VαMax marked with a protection symbol?
High-speed protection is a fixed speed (for example 330kt/M.86 plus 4 knots for A330).
Low-speed protection, on the other hand, is highly dependant on the G-load. If you fly manually and give a pitch input, the yellow/black tape (where the top marks V_ALPHA_PROT) and the red/black tape (where the top marks V_ALPHA_MAX) go up or down. The yellow line (V_LS) stays the same, as that speed varies with altitude and gross weight, not with G-load. This effect is even more pronounced at high altitude.
Therefore, a green mark would give the false impression of a fixed speed, as all the other single markings on the speed tape are fixed speeds (like green dot, S, F, V1, VR).