Blue and red line is an effect full of surprises, Incredibly fascinating, with an unexpected ending that will fool you.
Look carefully at the complete performance. The cards are shuffled so that red and black alternate, even face down and face up.
The cards magically unmix and then mix again by themselves, then a color change occurs on the faces and finally also on the backs.
In the explanation there is also a short tutorial on the techniques (false count) used.