Using colored pencils, is it better to ink the outline, or start coloring over it?
Color pencil considered as a light to dark application, thus tracing your initial sketch with any dark medium will ruin it (they will be visible beneath your painting, unless you intentionally want to do so like mixed ones) . So in my opinion you definitely  should not do that. Try to keep your pencil sketch as light as possible, barely can be seen. Then start with the lightest color / value and least pressure, continue by lying down darker tones gradually to build up the painting. 

You should preserve the light from the white of the paper or cardboard and you always can go darker but using an eraser will disturb both your pencil marks and the surface texture.