Completely natural colors!  New work I've done in "Bumble Bee" a travertine (NOT a jasper) that is mined from a hot springs fumarole at the base of a volcano in Java.  Most of this material has alternating dark stripes in it, hence the name.  I got one small chunk of this all yellow material that has touches of orange orpiment in it.  The yellow comes from sulfur in the water that deposits the layers of travertine in the fumarole.