Most of the brightly colored agate from Brazil (except green) will
fade on exposure to light since the dyes they use are apparently not
The brown, black and gray colors are natural and are stable. The
orange carnelian-like color is produced by heat treatment and is also
stable. Dyes used in other countries may be more or less stable. I do
not know of any way to prevent this fading but blocking UV exposure
should slow it down.