Please list below where the nectars are found in USUM
Yellow Nectar Melemele Meadow, during the night (6:00 pm - 6:00 am in Sun | 6:00 am - 6:00 pm in Moon) Pink Nectar Royal Avanue, during the day (6:00 am - 6:00 pm in Sun | 6:00 pm - 6:00 am in Moon) Red Nectar Ula'ula Meadow Purple Nectar Poni Meadow
Hope this helped.
you can find various coloured nectars at the island medows in glittering patches. if you attempt to "use" these on oricorio, its form should change. the purple nectar happens to be in the flower patch at the centre of the battle royal area.