LEGO® fans of a certain age will fondly recall the vintage 1960s/'70s LEGO logo that Francesco Spreafico is discussing today but may be surprised to learn it made further appearances in later decades, and even one in 2016. Francesco first published this article in Italian on his excellent blog Old Bricks.
The LEGO® logo has changed many times over the years, and around 1963-1965 they adopted the square shape that it still has today. Next to this square you could find another one, with a "rainbow" made of five coloured stripes: yellow, red, blue, white and black. These five colours were used together with the LEGO logo until 1973 and they kept using them for years even after that, without the LEGO logo.
But what are these colours? You might have read a few different explanations for them, but more often than not these explanations are incorrect or only partially correct.