I think you're right Steve. Meyerweissflog's aircraft, and others in the same paints, were probably not 74/75/76 as such, but so close that the colours later were refered to as such. I did see somewhere years ago that these colours, possibly/probably experimental at the time, did gain the RLM numbers later, although with slight changes, I think in the way of additives to aid preservation, which might have changed the hue ever so slightly.
As regards JG53 being an experimental unit, I haven't seen any 'official' documentation to this effect, but, from various sources, the concensus seems to be that they did have a number of 'non regulation' schemes, including various mottle patterns, and the greys, before other units eventually adopted them 'officialy'. This was also in operation during the period of the 'Red Ring' phase - maybe it was an extension of Goering's displeasure, deliberately messing them about with colour changes!!! (only joking, but you never know!).
The model I refered to is in fact the Airfix 1/24th scale '109E, which I picked up from good old Woolworths about 4 years ago, in the sale, half price at £7 !! I'm sure they must have got the full price wrong, as at the time it was still retailing at around £30 !! Anyway, as the undercart legs and attachment points were very 'softly' moulded, as was most of the kit, a sign of the age of the moulds, I decided to build it as a belly landed example, but wanted to retain the canopy. I'd already painted most of it as Meyerweissflog's machine, specualting a bit on what damage might have occured, when I got a pic of the aircraft here, on the forum. I was delighted to see that I was very close in the 'damage' I had modelled. I must get around to making a base for it, so that I can finish the darned thing!