Occasional prop_color_value set failure on MacOS

The following tests occasionally fail on my mac.

```
======================================================================
FAIL: Test if all the TVTK classes can be instantiated
----------------------------------------------------------------------
Traceback (most recent call last):
File "/Users/sborini/Work/github/mayavi/tvtk/tests/test_tvtk.py", line 669, in test_all_instantiable
raise AssertionError(message.format(''.join(errors)))
AssertionError: Not all classes could be instantiated:
Traceback (most recent call last):
File "/Users/sborini/Work/github/mayavi/tvtk/tests/test_tvtk.py", line 664, in test_all_instantiable
tvtk_klass()
File "tvtk_classes/hardware_selector.py", line 81, in __init__
tvtk_base.TVTKBase.__init__(self, vtk.vtkHardwareSelector, obj, update, **traits)
File "/Users/sborini/Work/github/mayavi/tvtk/tvtk_base.py", line 334, in __init__
self.update_traits()
File "/Users/sborini/Work/github/mayavi/tvtk/tvtk_base.py", line 482, in update_traits
setattr(self, name, val)
File "/Users/sborini/.jaguar/envs/jaguar/lib/python2.7/site-packages/traits/trait_handlers.py", line 172, in error
value )
TraitError: The 'prop_color_value' trait of a HardwareSelector instance must be a tuple of the form: (0.0 <= a floating point number <= 1.0, 0.0 <= a floating point number <= 1.0, 0.0 <= a floating point number <= 1.0), but a value of (1.0720514219217772e-35, 1.5052411792145747e-39, 9218721025359872.0) was specified.
Traceback (most recent call last):
File "/Users/sborini/Work/github/mayavi/tvtk/tests/test_tvtk.py", line 664, in test_all_instantiable
tvtk_klass()
File "tvtk_classes/open_gl_hardware_selector.py", line 44, in __init__
tvtk_base.TVTKBase.__init__(self, vtk.vtkOpenGLHardwareSelector, obj, update, **traits)
File "/Users/sborini/Work/github/mayavi/tvtk/tvtk_base.py", line 334, in __init__
self.update_traits()
File "/Users/sborini/Work/github/mayavi/tvtk/tvtk_base.py", line 482, in update_traits
setattr(self, name, val)
File "/Users/sborini/.jaguar/envs/jaguar/lib/python2.7/site-packages/traits/trait_handlers.py", line 172, in error
value )
TraitError: The 'prop_color_value' trait of an OpenGLHardwareSelector instance must be a tuple of the form: (0.0 <= a floating point number <= 1.0, 0.0 <= a floating point number <= 1.0, 0.0 <= a floating point number <= 1.0), but a value of (0.0, 0.0, -3.837566375786139e-11) was specified.
```