I don't think RAFG or NATO used YLO 1 and YLO 2.
I do have a tale about "Colour Boards".
This was at Main Met JHQ Rheindahlen c. 1978.
Methods were steam not electronic, colour states came in appended to obs and specials from all over Europe. MMO Rheindahlen conceived the idea of magnetic coloured Smarties on a metal sheet bearing a NW Europe map showing every airfield. P Met O went off to talk Workshops into cutting the metal, and his sidekick was despatched to buy the Smarties.
Came the Grand Christening. Jever is WHT said the assistant. WHT Smartie, up to board, release, thuds on ground. "Try another Smartie!" Thud. Thud ...
PMetO concluded "inverse square law, fablon plus map plus glue is too thick, Smarties too weak".
One assistant, braver than the rest, offered the thought that, although aluminium was a nice lightweight board, perhaps steel would be an improvement?
They were still sniggering 6 months later when I was posted in.