LCD display segments (pixels) are electrodes that are used to control the electric field applied to the liquid crystals that are between the electrodes. So in essence they are tiny capacitors, and to turn the segment on, a voltage is applied to electrodes to charge an electric field which quickly aligns the crystals to polarize the light so that it gets blocked in the polarizers so the segment looks black. To turn off the segment, the voltage between the electrodes is set to zero to discharge the electric field, which allows the liquid crystals to quickly unalign to remove light polarisation so the segment looks transparent again.
When the power is turned off, at some point the active display driving stops and the operation of the display driver might be undetermined due to the decaying supply voltage. It is possible that it allows the residual voltages to be applied to all segments of the column briefly or constantly to charge up the electric fields. Either way, the driver clearly does not discharge the fields to turn the segments actively off.
Therefore the segments remain aligned and will block the light, until the electrode voltage and thus the electric field starts to decay and the segment will slowly turn off. When only partial amount of the crystals are polarizing and blocking the light, the hue can be different. It is basically like looking at the display while slowly turning the contrast setting to zero.