Creating a Post-processor

I am creating a post-processor for a finite element program but I didn´t get a good quality of the images. I used the sequence of ideas below to create an image representing the specific result.

1) Creating the pallete of colors;

2) Creating a list where I use the fglBegin(GL_POLYGON), fglColor3f, and fglVertex2f functions to create the mesh´s elements and define a color for each element´s vertex.

3) Calling the list to create the image.

Inside the elements I didn´t get a good smoothing process between colors defined in each vertex. What I could do to improve the quality inside elements.

Thank you for your support.

Carlos A Santos.