Camouflage colours for British submarines according to the Dutch magazine Marineblad dated 1936 no. 5

An item referred to the magazine R.M. dated July 1936 reporting that experiments dealing the visibility of dived submarines resulted in camouflage patrons varying in which waters they operated. For the Atlantic Ocean, Mediterranean and the Red Sea were the colours to be grey green, sky blue and black. While the submarines were to operate everywhere was probably a camouflage combining the 3 patrons used.