I have found solution. I used pallette to add colors instead of surface.colors.add(..).
Thanks.

Hi,
I have been trying to resolve this problem for last two days.
I want to change the defaults colors in NTriangulatedSurfaceSeries chart which are shown in attached picture 1.
When I apply custom colors, I get chart shown in attached picture 2.
I want the same chart (picture 1) but filled with my own colors with no gradient effect.
Am I missing to set some field here?