I am not sure if they are green, I visited in early October. But a local tour group on Facebook mentioned a trip for a Light Festival there on the 29th of December. I don't know if there are other dates to see the lights, but if there are, that would be pretty amazing, I think.

First, you can go there by Bus from the Sasang Bus terminal(another name is Seobu bus termial) but that's not an express bus. It would stop four times on the way to go to Boseong. When you arrive at Boseong termial, you can take a bus at the same terminal. It takes 10~15 min. from terminal to greentea field. Sorry I can't remember bus number. Second, from Bujeon station. There is a train(mugunghwa) from Bujeon to Boseong station. And the same bus going to greentea field passes the Boseong station. If you have more questions, then ask me again.

Boseong Green Tea Festival will be held in May. Check out the exact date to visit there.

There is no bus commuting directly between Deajeon and Biseong. You should go to Gwangju and then go to Boseong from there if you want to use buses. Instead, you should go to Songjeongli Station on KTX (express train) and transfer to Mugugwha (slow train) going to Biseong Station. I hope is is helpful.