Hi John,
If you're referring to this camouflage scheme worn by Onslow:
It is the Special Emergency Fleet Destroyer Scheme, and though similar to the Western Approaches camo, used different colours:
Used by some fleet destroyers of the ”0” and ”P” classes from mid 1942, and then by other fleet destroyers as they entered service.
Colors used: G20, B30, G45, and white.
Decks: Steel areas are painted G20, Areas of wood, cemtex, corticene, and asphalt are left in their natural co1or.
Countershading: Paint the following white: Undersides of blast shields, flag decks, boats, Pom-Pom decks and other platforms.
I cannot find any pics of Onslow actually wearing Western Approaches camo, and doubt she did so.