What Color should that Polygon be?

There are four variables which determine how a polygon will be colored:
Color Selector, Illumination, Vertex type, and Facet Type.  The first
two are context attributes and the second two are per-primitive.

The Leo pipeline analyzes the values of these attributes and sets up
two variables called sp->surf.rend_color_src and sp->surf.rend_norm_src.

sp->surf.rend_color_src can have four values:
  CTX_COLOR:            Use the context color
  VERTEX_COLOR:         Use the color supplied with each vertex
  FACET_COLOR:          Use the color from the facet list
  FIRST_VERTEX_COLOR:   Use the color of the oldest vertex for each facet

sp->surf.rend_norm_src can have five values:
 NO_NORMAL:             No lighting, so we don't need a normal
 VERTEX_NORMAL:         Use vertex normals
 CALC_NORMAL:           calculate facet normals and use them
 FIRST_VERTEX_NORMAL:   Use oldest vertex's normal as facet normal
 FACET_NORMAL:          Use supplied facet normal

These values are assigned in LeoDataSelectors.cc.  A switch on
color selector and illumination in calcSurfCtxRenderOption
determines which function gets called (calcSurfRendCtxVertex
means color_source = context and ilum = per vertex, for example).
Within those functions there are switches on facet type and
point type, if necessary.

The following table summarizes how the values are determined:

-----------+-----------------------+-----------+-------+------
COLOR      |ILLUMINATION           |COLOR|NORM.|Color  |Normal
 SELECTOR  |                       |V |F |V |F |Used   |Used
-----------+-----------------------+--+--+--+--+-------+------
CONTEXT    |NONE                   |* |* |* |* |CONTEXT| -
           |ILLUM_NONE_INTERP_COLOR|* |* |* |* |CONTEXT| -
           |ILLUM_PER_FACET        |* |* |* |* |CONTEXT|FACET
           |ILLUM_PER_VERTEX       |* |* |N |* |CONTEXT|FACET
           |ILLUM_PER_VERTEX       |* |* |Y |* |CONTEXT|VERTEX
-----------+-----------------------+--+--+--+--+-------+------
FACET      |NONE                   |* |N |* |* |CONTEXT| -
           |NONE                   |* |Y |* |* |FACET  | -
           |ILLUM_NONE_INTERP_COLOR|* |N |* |* |CONTEXT| -
           |ILLUM_NONE_INTERP_COLOR|* |Y |* |* |FACET  | -
           |ILLUM_PER_FACET        |* |N |* |* |CONTEXT|FACET
           |ILLUM_PER_FACET        |* |Y |* |* |FACET  |FACET
           |ILLUM_PER_VERTEX       |* |N |N |* |CONTEXT|FACET
           |ILLUM_PER_VERTEX       |* |N |Y |* |CONTEXT|VERTEX
           |ILLUM_PER_VERTEX       |* |Y |N |* |FACET  |FACET
           |ILLUM_PER_VERTEX       |* |Y |Y |* |FACET  |VERTEX
-----------+-----------------------+--+--+--+--+-------+------
ILLUM_DEP  |NONE                   |N |N |* |* |CONTEXT| -
           |NONE                   |N |Y |* |* |FACET  | -
           |NONE                   |Y |N |* |* |CONTEXT| -
           |NONE                   |Y |Y |* |* |FACET  | -
           |ILLUM_NONE_INTERP_COLOR|N |N |* |* |CONTEXT| -
           |ILLUM_NONE_INTERP_COLOR|N |Y |* |* |FACET  | -
           |ILLUM_NONE_INTERP_COLOR|Y |N |* |* |VERTEX | -
           |ILLUM_NONE_INTERP_COLOR|Y |Y |* |* |VERTEX | -
           |ILLUM_PER_FACET        |N |N |N |* |CONTEXT|FACET
           |ILLUM_PER_FACET        |N |N |Y |* |CONTEXT|FACET
           |ILLUM_PER_FACET        |N |Y |N |* |FACET  |FACET
           |ILLUM_PER_FACET        |N |Y |Y |* |FACET  |FACET
           |ILLUM_PER_FACET        |Y |N |N |* |CONTEXT|FACET   #
           |ILLUM_PER_FACET        |Y |N |Y |* |CONTEXT|FACET   #
           |ILLUM_PER_FACET        |Y |Y |N |* |FACET  |FACET   #
           |ILLUM_PER_FACET        |Y |Y |Y |* |FACET  |FACET   #
           |ILLUM_PER_VERTEX       |N |N |N |* |CONTEXT|FACET
           |ILLUM_PER_VERTEX       |N |N |Y |* |CONTEXT|VERTEX  #
           |ILLUM_PER_VERTEX       |N |Y |N |* |FACET  |FACET
           |ILLUM_PER_VERTEX       |N |Y |Y |* |FACET  |VERTEX  #
           |ILLUM_PER_VERTEX       |Y |N |N |* |VERTEX |FACET
           |ILLUM_PER_VERTEX       |Y |N |Y |* |VERTEX |VERTEX  #
           |ILLUM_PER_VERTEX       |Y |Y |N |* |VERTEX |FACET
           |ILLUM_PER_VERTEX       |Y |Y |Y |* |VERTEX |VERTEX  #
-----------+-----------------------+--+--+--+--+-------+------
ILLUM_INDEP|NONE                   |N |N |* |* |CONTEXT| -
           |NONE                   |N |Y |* |* |FACET  | -
           |NONE                   |Y |N |* |* |VERTEX | -
           |NONE                   |Y |Y |* |* |VERTEX | -
           |ILLUM_NONE_INTERP_COLOR|N |N |* |* |CONTEXT| -
           |ILLUM_NONE_INTERP_COLOR|N |Y |* |* |FACET  | -
           |ILLUM_NONE_INTERP_COLOR|Y |N |* |* |VERTEX | -
           |ILLUM_NONE_INTERP_COLOR|Y |Y |* |* |VERTEX | -
           |ILLUM_PER_FACET        |N |N |N |* |CONTEXT|FACET
           |ILLUM_PER_FACET        |N |N |Y |* |CONTEXT|VERTEX
           |ILLUM_PER_FACET        |N |Y |N |* |FACET  |FACET
           |ILLUM_PER_FACET        |N |Y |Y |* |FACET  |VERTEX
           |ILLUM_PER_FACET        |Y |N |N |* |VERTEX |FACET
           |ILLUM_PER_FACET        |Y |N |Y |* |VERTEX |VERTEX
           |ILLUM_PER_FACET        |Y |Y |N |* |VERTEX |FACET
           |ILLUM_PER_FACET        |Y |Y |Y |* |VERTEX |VERTEX
           |ILLUM_PER_VERTEX       |N |N |N |* |CONTEXT|FACET
           |ILLUM_PER_VERTEX       |N |N |Y |* |CONTEXT|VERTEX
           |ILLUM_PER_VERTEX       |N |Y |N |* |FACET  |FACET
           |ILLUM_PER_VERTEX       |N |Y |Y |* |FACET  |VERTEX
           |ILLUM_PER_VERTEX       |Y |N |N |* |VERTEX |FACET
           |ILLUM_PER_VERTEX       |Y |N |Y |* |VERTEX |VERTEX
           |ILLUM_PER_VERTEX       |Y |Y |N |* |VERTEX |FACET
           |ILLUM_PER_VERTEX       |Y |Y |Y |* |VERTEX |VERTEX
-----------+-----------------------+--+--+--+--+-------+------
Y :There is VERTEX COLOR, VERTEX NORMAL, or FACET COLOR
N :There isn't VERTEX COLOR, VERTEX NORMAL, or FACET COLOR
* :Don't Care