Fireball's accessories were a purple frog brush
and a ribbon, as well as a puffy sticker. His brush is
distinctively more purple/lavender than that belonging to
set (see comparison below - Fireball brush pictured is
from my childhood pony.)
At present, no Mint on Card Fireball is
known to survive, so it is not possible right now to be one
hundred percent certain about his ribbon colour.
Fireball's Ribbon (Click to
expand)
The main problem with the Mountain Boys is that we have
very little concrete evidence to work with. There is only
so far that anecdotal evidence can take us.
No Mint on Card Fireball is known to survive, so all
evidence about his accessories are anecdotal, including
the ribbon. The most commonly cited ribbon colour for
Fireball is peach-orange. This ribbon looks near identical
to that which is included with at least two Sunbursts Mint
on Card.
Could Hasbro have used the same ribbon for two ponies?
Well, yes. The Princess Pony release gives us a precedent
for this, with Amethyst being sold predominately, if not
exclusively, with Sapphire's hat.
But at the same time, the Princess Ponies give us another
important message about ponies and accessory releases in
the UK. There are known accessory variations in the
Princess release here (notably with wands), and this may
well be because the set was sold in both 1987 and 1988.
The same conundrum exists with the Mountain Boys, albeit
with far less material to theorise with. The Mountain Boys
were only on sale in the UK in 1987. They were then on
sale in Nordic countries in 1988. Like the Princesses,
they were produced and packaged over a two year period.
To my knowledge, all surviving Mint on Card Mountain Boy
ponies originate from Nordic countries. This means that we
have no surviving examples of 1987 carded Mountain Boys or
anything from the UK release except collector memory. In
one example, one person recalled Fireball having an
orangey ribbon and Sunburst a yellow one. Another source
suggested those colours but in reverse. Since the existing
Mint on Card Sunbursts indicate a peach-orange ribbon, it
seems most likely that if any Mountain Boy had a yellow
ribbon, it was Fireball.
I am not ruling out the possibility that Fireball and
Sunburst had basically the same ribbon (minor shade
differences can be attributed to batch or fading). But it
is also possible that Fireball had a completely different
ribbon, and this knowledge has been lost with the rest of
the UK evidence over time.