The green stuff is this stuff called GroGel that came with the brooder kit I bought (also had light, thermometer, food and water containers). It is a powder and you mix it with water - it has amino acids and protein and carbs and obviously also moisture so they recommended it for new mail order arrivals to help them get a boost after the journey. They seem to like it - they basically are pecking at enything and everything - including each others toes for the first 15 minutes or so. One of the EE chicks (brown speckly one) seemed fairly out of it when I first unpacked her, but once she got some water and some gel and a few minutes later she perked up and has been drinking and eating now along with everyone else.
The yellow chick (also supposed to be an EE) was really picking on everyone else for awhil but things seem to have calmed down now.