Why do locust trees have red marks inside?

Locust trees, particularly black locusts, have red markings on the inner bark and wood due to the presence of tannins and other pigments. These compounds can provide protection against pests and pathogens, contributing to the tree's resilience. The red coloration can also be an indicator of the tree's age or health. Additionally, the distinctive red hue can enhance the aesthetic appeal of the wood when used in woodworking.