SolidColoredTriangle

import vtk

# setup points and vertices
Points = vtk.vtkPoints()
Triangles = vtk.vtkCellArray()

Points.InsertNextPoint(1.0, 0.0, 0.0)
Points.InsertNextPoint(0.0, 0.0, 0.0)
Points.InsertNextPoint(0.0, 1.0, 0.0)

Triangle = vtk.vtkTriangle()
Triangle.GetPointIds().SetId(0, 0)
Triangle.GetPointIds().SetId(1, 1)
Triangle.GetPointIds().SetId(2, 2)
Triangles.InsertNextCell(Triangle)

# setup colors (setting the name to "Colors" is nice but not necessary)
Colors = vtk.vtkUnsignedCharArray()
Colors.SetNumberOfComponents(3)
Colors.SetName("Colors")
Colors.InsertNextTuple3(255, 0, 0)

polydata = vtk.vtkPolyData()
polydata.SetPoints(Points)
polydata.SetPolys(Triangles)

polydata.GetCellData().SetScalars(Colors)
polydata.Modified()
if vtk.VTK_MAJOR_VERSION <= 5:
    polydata.Update()

writer = vtk.vtkXMLPolyDataWriter()
writer.SetFileName("TriangleSolidColor.vtp")
if vtk.VTK_MAJOR_VERSION <= 5:
    writer.SetInput(polydata)
else:
    writer.SetInputData(polydata)
writer.Write()