
The four dimensions are rendered using color as well as conventional perspective. Since color forms a three-space, the fourth dimension is projected into it at an angle. The four dimensions are rendered as (Red, Green, Blue, White).
Of course, it's possible for the tesseract rotate lots of different skewed ways that aren't pictured individually here - but any such motion can be expressed as a linear combination of these 6 rotations.
You might also enjoy the companion video (), which shows construction of the tesseract from a point by multiple extrusions.