Pastels vibrate and shimmer like no other painting medium.  They are virtually pure pigment.  With little
or no binder to hold them together they stack up on the surface. There is no sheen to the matt ground of pigment resulting in explosive color. 
I like to push them into the surface forcing them to have a three dimensional quality. Color-wise they behave like stained glass.  If you want
to learn about color,
study pastels.