The colorfastness of black fiberglass tissue is typically high, as it is designed to resist fading and color changes under various conditions. It is resistant to light, washing, and heat, maintaining its color integrity even after prolonged exposure or repeated use. This makes it suitable for applications where color stability is crucial, such as in construction materials, automotive parts, and other industrial uses. However, the exact level of colorfastness can vary depending on the specific manufacturing process and the quality of the fiberglass tissue.