Out of the blue refers to the second glider created by the natural Heisenburp, or in general, a second spaceship created during a Heisenburp reaction. Other similar mechanisms, particularly the method of LWSS creation used in the pixel part of the OTCA metapixel, may also be referred to as "out of the blue" reactions.
The LWSS-generating mechanism with HWSSes passing by a period-46 sparker, as employed by the OTCA metapixel (click above to open LifeViewer) RLE:herePlaintext:here