newbie first trip question

Hi All

We just got a new 2013 2720 and are on our First outing. Learning things along the way. For one thing, need to practice trailer reversing! And note to self - bring firewood. More on our first trip later, but now for a question - How do you read the holding (gray water) monitor? Our has green light at the bottom then a yellow light then two red lights. We've been here least than one day. Please advise - sorry for such a simple question. Thanks in advance

Sancyn