I think that all the earlier coated lenses had the blue-purple cast. The multi-coated tend to appear amber and purple at the same time, almost irridescent. I have seen some lenses that have somewhat of a blue-green reflection. The reflected color you see does not color the image as far as I can determine. When you look through the lens you see a clear image and not the color tint that is so obvious in the reflection.

This is way over my head.