Natural dye will change. That is the point.

A synthetic dye is engineered to sit still. A natural dye is not, and the change it goes through is the reason people who wear it keep wearing it. Madder root gives a red that moves warmer over roughly the first year and then stabilises. Indigo deepens for about six washes as the pigment oxidises further into the yarn, then holds for years. Harad — myrobalan — shifts toward gold in a way that is most visible against ivory. What all of this asks of you is only that you wash in cold water and dry in shade. What it gives back is a garment that looks like it has been lived in rather than one that looks tired.