I think there are three differences between evergreen and evergreen:
1. The purpose of words. "Evergreen" emphasizes the never-fading nature of green leaves. "Eternal" describes persistence and immortality.
2. Describe the object. "Evergreen" focuses on describing plants, while "Eternal Evergreen" describes people or a certain kind of thought or culture.
3. Meaning of use. "Eternally green" implies that it is not affected by time and environmental changes. And "evergreen" implies that it has been spread for a long time in the long history.