Where are they, also, do they respawn, cause I got the Red ones and I haven't seen them come back ever.
You use the Red nectar for the Baile Style, Yellow for Pom-Pom, Pink for Pau'u and Purple for Sensu. You get 2 red nectars in the Ula'Ula meadow daily twice. You get the pink nectar on royal avenue. You get the purple nectar at the Poni Meadows. You get the Yellow nectar at Melemele meadow.
Source: Experience and all Bulbapedia articles on oricorio and the nectars
Hope this helps :)