When hair is created, Start curves are created automatically. If Create Rest Curves was turned on in the Create Hair Options window, then Rest Curves are created as well. If not, then you can create Rest Curves at any time using the Start or Current Position curves. When you play the simulation, the Current Position is what you display to see the hairs react to dynamic forces.
When creating curves for hair, Rest and Current Position curves are initially colored brown and blue, respectively, to help distinguish them from Start Position curves. This is done using the Draw Overrides on these curve nodes. Layers depend on Draw Overrides as well; therefore, if you create the hair in a layer or add it to a layer, then the color of all hair curves is now the same, even if the hair is subsequently removed from the layer.
While modeling hair, you may reset the Start or Rest curve positions several times.
