If you wanted a green Land Rover with a tin cover in the early days you would have to get Gift Set No.2. The normal boxed ones were either yellow with a black roof or blue with a white roof. For 7/9d you got the 4/- Pony Trailer and pony, the 3/6d Land Rover and I guess the extra 3d was for the cover!
Now, most Pony Trailers you'll come across will be bright red with a black chassis but some very early ones were a pale shade of pink-cream with a red chassis so the set about is actually quite difficult to find for several reasons.
The later type of Land Rover appears in 1961 and sets get the green one with its cream plastic cover, pulling a red horsebox. The horsebox is unchanged for a while, other than the pale cream version not being around.
Change does come quite soon, though, and a new fawn colour Pony Trailer is issued. This has the same box affair but sits on a different chassis, incorporating a solid tow bar. It matches perfectly the new colour of Land Rover too, which also gets red seats now in place of the yellow ones in the green Land Rover.
A few examples do exist of the green Land Rover with red seats. I have one with an original box but it is one of my most expensive models. they are extremely difficult to find but you may strike lucky as not every seller realises the difference.
The fawn colour looks good in the set but individual Land Rovers in that colour always seem to look a bit tired. Maybe it is just those that I have acquired! They just don't look as smart as the green ones on their own. These did stay around for many years, though, before Gift Set No.2 becomes Gift Set No.15 and everything turns blue.
The Pony Trailer is now a much bigger thing with room for two ponies - supplied with a big one and a little one. There are two ramps, with nice cork covering and a divider inside. The Land Rover turns a matching shade of blue and has a white cover now, with Corgi Pony Club decals (missing here).
This is also the time of changes to the wheels and this set can be found with cast wheels, as illustrated here, plain wheels on some of the early editions of the set and, on late editions, Whizzwheels.
Whilst the Land Rover continued to have all sorts of different shades of paint thrown at it over the years (about which I have written separately) the Pony Trailer only had the three variations for #102 and just the blue and white for #112.