The resistance to light and washings of natural dyes might not the same that the one achieved with synthetic dyes, although we all know that prolonged exposure to the sun and washing wear away any color. Therefore, we recommend you to wash your garments by hand, with a delicate neutral soap and let them dry in the shade on a smooth surface.
Natural dyes are very sensitive to pH, so it is important to follow this recommendation to keep the colors unchanged. However, some pigments may vary slightly in shade over time precisely because the natural color remains "alive". Please consider this as the beauty of nature.
Also, wash your clothes only when necessary, just by simply airing the garment is enough for the fibers to regenerate.