Are mung beans still good to eat if they are turning purplish?

I've tried sprouting mung beans multiple times and I am able to eat some but they start to turn a purplish color pretty fast and I'm not sure if they are still good to eat. For example I started sprouting some 3 days ago and yesterday they were still too small to eat, today they are big enough to eat but are already turning purple. What causes this and are they still good to eat?