The Wilton colors used for buttercream, can I use these on gumpaste also, or should I purchase the color dusts? thanks a bunch!!

Yes, the gel colors can be used to color gumpaste.

Yes, paste/gel colors are used to color any icing medium.
Dusts are used on finished pieces to add color hightlights - not so much for 'total' coloring that gels give. Dusts are not mixed into icing mediums - just dusted on.