How can there be green nodes for a binary attribute like gender?
The colors represent the values contained in a node, thus for a binary attribute like gender, green matches a value of 0.5 (i.e., 50% of the data records in the node are female, the other 50% are male). Of course all colors are possible depending on the percentage of female in a node. The less priority you give to a binary attribute the more colors you might see in the picture of that attribute since the data will not necessarily be ordered in, for example, male and female (leading to mostly blue or red nodes) but males and females might rather be evenly distributes over the map.
