Most definitely persevere with LAVENDER GREY.
It was on my short list of choice to repaint my XK140, being one of my preferred GREENS along with Pastel Green and BRG.
And that’s how I best describe it. It is a GREY, but the tones are definitely Green, thus the most common trim combination offered by Jaguar was SUEDE GREEN which really brings out the compatible green tones in the GREY. (Why on earth this colour was called LAVENDER GREY is anyone’s guess, not that a colour name is exact science at the best of times)
My suggestion is if your car was originally Lavender Grey, have a good look around car for signs of original colour. (In the doors, boot-lid, luggage compartment, spare wheel tray etc) Its most unlikely when your Mark V was repainted it was a 100% body off strip and repaint removing all traces of original colour.
Otherwise, I do have one of the exceptionally rare ZOFELAC (Cellulose Enamel) Paint Chip booklets, which is the exact same paint/colour as was used originally for Mark V (and XK120) prior to the Synthetic Enamels introduced in 1952 with LAVENDER GREY continuing to be a standard Jaguar colour name and shade.
There have been a number of efforts to exactly match both the ZOFELAC Lavender Grey and the Synthetic Enamel Lavender Grey (to my eyes the same, but to a colour experts maybe not 100%), but it should be appreciated there are other factors that have a major influence on the appearance of the end paint colour, and indeed there are variations paint brand/formula to paint brand/formula - thus best to match an original sample or original Zofelac paint-chip book. Really depends a lot on just how accurate you want to be, or just ‘near enough’, and indeed the skills of your painter and colour matcher and colour system used.