#I haven't read enough arthurian lit to start seriously psychoanalyzing characters yet

[liminalpsych]

Theory: Gawain's horse Gringolet was an Eriskay pony.

Source for Gringolet's coloring: This excellent blog post, Sir Gawain and the Grey Gringolet.

“They brought Sir Gawaine a steed,

Was dapple gray and good att need,

I tell withouten scorne” [268-70, The Greene Knight]

Wikipedia's entry on Gringolet says, "More generally accepted is the suggestion by the prominent Arthurian scholar Roger Sherman Loomis that the French name Gringalet derived from either the Welsh guin-calet ("white and hardy"), or keincaled ("handsome and hardy")."

So he's dapple gray or he's white. (Possibly "linked to a wider Celtic tradition of white horses with red ears." Not important for the purposes of this post.) Both can be true, since true "white" horses are rare; generally they're gray and have whitened as they've gotten older. Thus young Gringolet could be dapple gray while older Gringolet could be white. (It really doesn't take long for them to get really white looking.)

Back to the Eriskay ponies! We know from a recent comprehensive archaeological study that medieval knights rode ponies. Horses that were under 14.2hh / 4'10" / 1.47 meters at the shoulder or smaller. Which is probably about 950 lbs / 430 kg or smaller (weight is based on my 14.2 horse, who's built pretty drafty and heavy boned, and is 950 lbs when he's not too chonky).

Eriskay ponies are between 12 and 13.2 hh (4 ft to 4 ft 6 inches, or 121.92 cm to 137.16 cm) at the top of their shoulder, which is closer to the average of horses at the time of King Arthur and Sir Gawain.

They're from the Outer Hebrides islands in Scotland, originally the Isle of Eriskay. They have long been protected from outside influence by their island location, and so the Eriskay ponies of today are probably pretty close to the ones of the 5th century, at least closer than any of the other native ponies of England, Scotland, etc. Here's a map I found on a Google search of the Scottish islands. The Orkneys, where Gawain would have been from in later Arthurian literature*, are 18-20 at the top/north of the map. Eriskay is in the Outer Hebrides, a tiiiny isle between South Uist (16) and Barra (17) on the far left/west of the map. So not exactly the same place, but close enough, relatively speaking. And I couldn't find anything on native horse breeds of the Orkneys.

* He wasn't from Orkney in the early literature, he was of Lothian. His father was Loth of Lothian, which is in southeastern Scotland in the lowlands, and Loth was later King of Norway in Geoffrey of Monmouth's History of the Kings of Britain, supposedly by right of being nephew of the former king. Orkney was a separate kingdom with its own king. But he's most popularly associated with Orkney in later literature and in modern fandom, so we're going with it.

Other native Scottish breeds include:

Galloway pony. If this one came in gray, I'd say it's as likely as the Eriskay (especially as Gawain was originally from what is now southeastern Scotland in the early literature aka Geoffrey of Monmouth's work), but it was usually bay or black. Now extinct as a breed, unfortunately. Noted for its “good looks, a wide, deep chest, and a tendency to pace rather than trot", which would have been an advantage on long rides. From Scotland and northern England. Small head and neck, elegant build, eventually absorbed into the Fell pony.

Shetland pony. I think they were probably a little small even for shorter medieval knights. They're 3.3 feet tall at the shoulder maximum. That's 10 hh or about 1 meter tall. 300-500 lbs or 135-225 kg.

Highland pony. They are usually various shades of dun, and taller than the other ponies, and do sometimes show up in dapple gray. We have fewer records and evidence of its history though; we have some descriptions in the 18th century of what's believed to be Highland ponies, but that's about it. I'll accept arguments for some old variety of the Highland pony as Gringolet, but remember that we're looking at the late 5th century, so the late 400's C.E., and I think the modern Highland pony is not going to provide a useful model of whatever Gawain was riding back in the 5th century.