A box can be 'opened' by right-clicking the mouse on its front face. The 'inside' of the box will show the colors of the faces opposite to those that are visible on the 'outside', (the back, right and bottom sides).
Depending on the type of game being played, positional information or a helpful hint might also appear within an opened box. For example, in a Jumbled Cube or Jumbled Pyramid game the presence of a Bonus Box or Bad Box might be revealed before it is actually selected by clicking the mouse.
To 'close' an opened box, right-click it again with the mouse.