The array is in a format that can be directly used in BaseChart.gradientColor2 and DrawArea.gradientColor2. Its contents (in hex) is:
00 9898E0 60 F0F0FF B0 D8D8F0 100 9898E0
See Color Specification on how colors are represented in ChartDirector.
ChartDirector 5.1 (PHP Edition)
phpchartdir.blueMetalGradient
Description