Can't color a XML Unstructured Grid (*.vtu)

VR/AR
3

Thanks alot for reply.

Sorry I forgot to explain what color_range is.
It has following syntax: Color color_range(double Percentage)
I specify percentage as

(cells.GetComponent(i, j) / cell.GetArray(i).GetRange()[1]) * 100

and it returns color range from blue to red.
Its filled inside c variable.
For interpolation, I use following code: Color Interpolation Between 3 Colors in .NET - Stack Overflow

Even if I override c and set its value as c = Color.Blue, it would show the same gray color.

But strangely, the same code works fine for vtp, vtk.
Just it fails for vtu files.