red, green, blue
Set the plane color, between black (0.0, 0.0, 0.0) and white (1.0, 1.0, 1.0).
Example: <plane ... red="1.0" green="1.0" blue="0.0"/> (default)
(defined in GAMGI_MESA_PLANE_R, GAMGI_MESA_PLANE_G
and GAMGI_MESA_PLANE_B)
Allowed values: 0.0 - 1.0 (optional, coupled)
scale
Change the plane size, including its child objects. Plane objects are
scaled around the plane center. The visual representation of an object
is always scaled by its own scale factor multiplied by the scale factor
of all its parent objects until layer, inclusive.
An error is shown when plane 
type is 
pole, 
trace
(stereographic projection) or 
reciprocal (reciprocal lattice) or 
when 
autonomy is 
no (plane cannot scale independently of 
its parent).
Example: <plane ... scale="1.0"/> (default)
(defined in GAMGI_MESA_SCALE)
Allowed values: positive real (optional)