2. Normals -- recalculate inside.
The player will be inside the SkyBox and we want the sky to be displayed on the inside where the player can see them.
Cube selected. Edit Mode.
3D View menu >> Mode Box >> Edit Mode
Select all vertices/edges/faces.
3D View menu >> Select >> Select/Deselect All
Normals: recalculate inside
3D View menu >> Mesh >> Normals >> Recalculate Inside
Ctrl Shift N
Recalculate normals inside