The Merry-Go-Round Ponies in the UK and Europe
The Merry-Go-Round Ponies were carousel-themed earth ponies
with moulded patterned capes with a raised design of flowers,
diamonds or hearts. They were introduced in the UK comic in a
weird multi-part story about a Whispering Whirligig, and soon
made Ponyland their fairground home. Each came with a flower
brush and no ribbon. They were sold in box rather than on card.
The Merry-Go-Round ponies were released in North America in 1989,
as a set of six. In 1990, four of these characters were released
in the UK and in Europe, although there was a colour variation
between packages in the UK and in some European countries.
Although both box styles feature Mainsail under the rainbow -
proof that they were both sold in 1990 - boxes in the UK had blue
borders, while those in France and Spain had purple (examples
shown below). I am not sure about other European countries, or why
this packaging difference happened.
Sunny Bunch Mint in Box
UK, 1990
(Colour palette - blue)

Flower Bouquet Mint in Box
Spain, 1990
(Colour palette - purple)
Image donated by ebay seller.
Sunshine Ponies in North America - Two Extra Friends
Although the release of the Merry-Go-Round Ponies in the UK and
Europe contained four ponies, the wider set sold in 1989 in North
America included two additional characters - Sparkler and Diamond
Dreams. These two ponies shared a pose and a cape style.
Diamond Dreams, Mint in Box
US style box, 1989
Image from Shivhae
The boxes in North America were quite different from those in the
UK and Europe, but the tagline on the US and UK boxes were more or
less the same.
I currently have no evidence to suggest that this was one of the
sets that Woolworths imported into the UK from North America.
Although I found my Diamond Dreams here loose at a carboot sale, I
have never found Sparkler, and have never seen any others. It is
possible that the full set were available somewhere in Europe, but
I have no evidence for this right now either.