The Colors are enumerated values.  


Fig.Plot(1..10).Signal(1..10).Color = eColor


eColor: (Enumeration)  Blue, Green, Red, Magenta, Yellow, Purple, Orange, Cyan, Black


If you do not specify a Signal color then the default will be used.
The default order can be can be set in the Default Configuration


Enum eColor

    Blue = 0

    Green = 1

    Red = 2

    Magenta = 3

    Yellow = 4

    Purple = 5

    Orange = 6

    Cyan = 7

    Black = 8

End Enum