Level Band_ Display issues

Hi Team,

When I try to get a level bands for Isopachyte (Between Design surface and Existing ground) am unable to get the level bands as in prescribed format i.e. with different colors for each level difference range. Instead am getting as a white triangular lines.

For easy understanding am attaching screen shot.

Kindly suggest me the correct way, if am doing anything wrong or if its a display issues how to correct it.

Thanks for the any help which you can give on this.