What does "Green is the new black" mean?

Native speaker’s answer
Rebecca
"Green is the new black" means that the colour "green" has replaced the trend of the colour "black". So, black is no longer in style, but green is! You can apply this phrase when talking about other trends as well. Ex: You should know, baggy jeans are the new skinny jeans these days! Ex: Working in comfortable clothes is the new business casual while working remotely.