I have always assumed that Woden rode a grey horse for it is written in the Eddas that Odin's horse Sleipnir was grey:
"It was grey and had eight legs, and this is the best horse among gods and men." (Gylfaginning, Prose/Younger Edda, translated by Anthony Faulkes)I have checked all the references to Sleipnir in both the Elder and Younger Eddas and I can only find this one reference to his colour. It needs to be born in mind though that the composition of this Edda was relatively late. Snorri Stuluson composed this work around the year 1200 CE so we cannot tell how ancient the concept of a grey Sleipnir is. We also do not know whether Snorri obtained this information from an earlier source as Sleipnir's colour is not mentioned in the Poetic/Elder Edda which was composed possibly as early as the 10th century although it is incorrectly attributed to the 12th century Icelandic priest Saemand the Learned. It is thought by scholars that the Elder Edda contains genuinely ancient material and most if not all of it would have been familiar to people in the Viking Age so it is curious that the colour of Odin's horse is not mentioned in these early poems.
What has caused me to question the colour is due to a rereading of parts of Jacob Grimm's Teutonic Mythology Volume 1:
"We are expressly told, this wild hunter Wode rides a white horse." (page 156)
"In S. Germany they tell of the lord of the castle's grazing gray (or white), Mone anz. 3, 259 ; v. infra, the 'wuetende heer'."
Grimm refers to various legends from Mecklenburg regarding the Wild Hunt whose leader is known as Wod which my readers will be aware that along with its variant Wode is the oldest name of our High God:
"A peasant was coming home tipsy one night from town, and his road led him through a wood; there he hears the wild hunt, the uproar of the hounds, and the shout of the huntsman up in the air: 'midden in den weg!' cries the voice, but he takes no notice. Suddenly out of the clouds there plunges down, right before him, a tall man on a white horse." (Teutonic Mythology volume 3, page 924)
I will not repeat the entire story here but refer my readers to Grimm but it should be noted that the 'tall man' is referred to as Wod in the rest of the tale. However it should be noted here that Wod rode a white horse, not a gray one and I believe that this was the original colour of the horse whether it was eight legged or not (this may be a later development). Likewise the name of the horse, Sleipnir was probably a later and more northerly development.
Of course whilst this information may in itself be interesting my readers will be wondering why I have posted this here rather than on my Celto-Germanic Culture, Myth and History blog. The reason for this will become clear. According to the Purana Hindu scriptures Kalki will ride a white horse and carry a blazing sword. Like Sleipnir it is a horse that is capable of riding through the air.
"Lord Kalki, the Lord of the universe, will mount His swift white horse Devadatta and, sword in hand, travel over the earth exhibiting His eight mystic opulences and eight special qualities of Godhead. Displaying His unequaled effulgence and riding with great speed, He will kill by the millions those thieves who have dared dress as kings." (Srimad-Bhagavatam (12.2.19-20)
White horses had a particular mystical significance for the Germanic peoples and were used for purposes of divination:
"Peculiar to that people, in contrast, is to try as well the portents and omens of horses: maintained at public expense in the groves and woods, they are white and untouched by any earthly task; when yoked to the sacred chariot, the priest and the king or leading man of the state escort them and note their neighs and snorts. To no other auspices is greater faith granted, not only among the common folk, but among the nobles and priests, for they see themselves as mere servants of the gods, but the horses as their intimates." (Germania 10:2, Tacitus, translation by J.B. Rives)
"Although the familiar method of seeking information from the cries and the flight of birds is known to the Germans, they have also a special method of their own-to try to obtain omens and warnings from horses. These horses are kept at the public expense in the sacred woods and groves that I have mentioned; they are pure white and undefiled by any toil in the service of man. The priest and the king, or the chief of the state, yoke them to a sacred chariot and walk beside them, taking note of their neighs and snorts. No kind of omen inspires greater trust, not only among the common people, but even among the nobles and priests, who think that they themselves are but servants of the gods, whereas the horses are privy to the gods' counsels." (Germania 10, Tacitus, translation by H. Mattingley, revised by S.A. Handford)
As my English readers will know the English countryside in the south of the country has various chalk images cut into the sides of hills and some of these are of horses such as the Uffington Horse which is said to date back to the Bronze Age. The Westbury Horse is another example which certainly goes back to at least Saxon times. The flags of Kent and Niedersachsen in Germany feature a white horse. The chieftain brothers Hengest and Horsa likewise have names that are equine in nature. Thus the White Horse had a clear mystical importance in the culture and psyche of pre-xtian Germanic man. It was also revered by the Celtic peoples. The Goddess Rhiannon who features in the Mabinogi, rides a 'pale' horse and She may be associated with the Gallo-Roman Epona. In Slavic mythology the God Svantovit owned an oracular white horse. In Greek mythology the God Poseidon fathered a winged white horse, Pegasus.
We should not be surprised that the horse, especially the white one was held in such high esteem as the Aryan peoples accorded a solar origin to this noble beast:
"The horse figures with the bull-ox, stag and aquatic birds in proto-Celtic cult contexts and, as examples from Scandinavia show, it had, at this stage, definite solar associations.
"In Indo-European contexts, the horse was of great economic and ritual importance, and its cult role amongst the Celts reflects this widespread attitude. Its importance is demonstrated, for example, by the coins, on which it may be figured alone or in company with the charioteer-often a crane appears above or below it, as in the symbolism of the Urnfield and Hallstatt toreutic tradition." (Pagan Celtic Britain, 1967, Anne Ross)
The book of Revelation refers to a white horse in two chapters:
"And I saw, and behold a white horse: and he that sat on him had a bow; and a crown was given unto him: and he went forth conquering, and to conquer." (Chapter 6, verse 2, AV)
"And I saw heaven opened, and behold a white horse; and he that sat upon him was called faithful and true, and in righteousness he doth judge and make war." (Chapter 19, verse 11, AV)
It is more than clear to me that regardless of that single reference in the Younger Edda the colour of Woden's horse is white and the colour matters because this ties him in with the Kalki avatar and the figure(s) referred to in Revelation 19. However we know from the Eddas that it is not Woden Himself that is coming but His son and avatar Widar. When Widar takes His place at Ragnarok He will mount a horse and I believe that this will be the horse of His father, Woden. It makes sense for all sorts of reasons.
"Brushwood grows and high grasswidely in Vidar's land;
and there the son proclaims on his horse's back
that he's keen to avenge his father.
(Grimnismal 17, Elder Edda, translation by Carolyne Larrington)