The array is in a format that can be directly used in BaseChart.gradientColor2 and DrawArea.gradientColor2. Its contents (in hex) is:
00 98E098 60 F0FFF0 B0 D8F0D8 100 98E098
See Color Specification on how colors are represented in ChartDirector.
ChartDirector 5.1 (PHP Edition)
phpchartdir.greenMetalGradient
Description