If you hover the color boxes with the mouse cursor you will find that the responsible python struct is UserSolidLight
with the following properties
base class — bpy_struct
class bpy.types.UserSolidLight(bpy_struct)
Light used for OpenGL
lighting in solid draw mode
diffuse_color
Diffuse color of the OpenGL light
Type: float array of 3 items in [0, inf], default (0.0, 0.0, 0.0)
direction
Direction that the OpenGL light is shining
Type: float array of 3 items in [-inf, inf], default (0.0, 1.0, 0.0)
specular_color
Color of the light’s specular highlight
Type: float array of 3 items in [0, inf], default (0.0, 0.0, 0.0)
use
Enable this OpenGL light in solid draw mode
Type: boolean, default False
According to the Python API Documentation