1. ISABELLA colour.
I have to apologize. I wrotte a wrong link. The right one is : http://colorscavalls.feshocat.cat/articleIsabel.html
The theory is old and not OK but the article offers some good information including the mention of the Bibliotèque Veterinaire de Lyon.
A resume of my last theory is :
The anonymous book "Pintura de un potro" ( circa 1670 )was published by the Sociedad de Bibliofílos Españoles in 1877 ( Bañuelo y de la Cerda, Luís ) toghether with "Libro de la Jineta y
descendientes de los caballos Guzmanes".
This work classifies the Isabella coats among the "baios" and says :"...son vistosos los de color de ysabella, colas y clines alheñadas y lueñas...".
That is : ( among the buckskin coats )...the ones with the color of the ysabella are eye apealling , with long and reddish manes and tails...This is a description of perlino coats.

The use of the "de" is very clear. Imposssible for a Castilian knight to use with the name of the greatest Castillian queen.
In my opinion this color of the ysabella is related with the plant "Malva isabela" with white flowers somewhat reddish.
"Malva isabella" is the marshmallow plant whose roots were at the origin of the mashmallow cakes.
A search of old Spanish, French and English treatises is needed to verify this possible relationship ( Bothanics , Pharmacy, Dyes ,...etc).

2.HORSE NAMES.
Try this link : http://www.websters-online-dictionary.org/definition/horse

A resume :

Alfana. ((( Should be Alfara ? ))) Gradasso's horse. The word means "a mare." (Orlando Furioso.
Aquiline (3 syl.). Raymond's steed, bred on the banks of the Tagus. The word means "like an eagle." (Tasso: Jerusalem Delivered ).
Arundel. The horse of Bevis of Southampton. The word means "swift as a swallow." (French, hirondelle, "a swallow.")
Babieca (Spanish, "a simpleton"). The Cid's horse.
Bajardo. Rinaldo's horse, of a bright bay colour
Bayard. The horse of the four sons of Aymon
Bevis. The horse of Lord Marmion. The word is Norse, and means "swift." (Sir W. Scott.
Brigliadoro [Bril-ya-doro]. Orlando's famous charger, second only to Bayardo in swiftness and wonderful powers. The word means "golden-bridle." (Orlando Furioso, etc.)
Bronzomarle (3 syl.). The horse of Sir Launcelot Greaves. The word means "a mettlesome sorrel."
Ferrant d'Espagne. The horse of Oliver. The word means "the Spanish traveller." (( I don't agree. "Ferrant" meant "blue roan" or "iron grey" ))
Frontaletto. Sacripant's charger. The word means "little head." (Ariosto: Orlando Furioso.
Frontino or Frontin. Once called "Balisarda." Rogero's or Rugiero's horse. The word means "little head." (Ariosto: Orlando Furioso, etc.)
(( Frontino and frontaletto indicates a white frontal marc ))
Grane (2 syl.). Siegfried's horse, of marvellous swiftness. The word means "grey-coloured."
Lamri. King Arthur's mare. The word means "the curveter."
Orelia. The charger of Roderick, last of the Goths, noted for its speed and symmetry
Passe Brewell. Sir Tristram's charger. (Hist. of Prince Arthur, ii. 68.)
Rabicano or Rabican. Argali'a's horse in Orlando Innamorato, and Astolpho's horse in Orlando Furioso. The word means a horse with a "dark tail but with some white hairs."
Spumador. King Arthur's horse. The word means "the foaming one."
Suleiman. The favourite charger of the Earl of Essex.
Tachebrune (q.v.). The horse of Ogier the Dane.
Trebizond. The grey horse of Admiral Guarinos, one of the French knights taken at Roncesvalles.
Vegliantino [Vail-yan-te'-no]. The famous steed of Orlando, called in French romance Veillantif, Orlando being called Roland. The word means "the little vigilant one."
White Surrey. The favourite horse of King Richard III.
"Saddle White Surrey for the field to-morrow." Shakespeare: Richard III., v. 3.

"....To Alice my wife all the ostilments and utensils belonging to my house; to the same Alice 3 horses, one called "Brok", the second "Bayard" and the third "Hobbe", 7 cows, a cart, a tumbrel and 2 ploughs......" etc.

Lyard = grey , dapple grey
Bayard = from Bay
Ferrault = ? ( Probably derivated from Ferrant , litterally "iron colour" = blue roan or iron grey )

2.
year 1298
Roll of Horses. Battle of Falkirk.
edited by Henry Gough (Westminster, 1888)
ROLLS OF THE HORSES. Interfectus in foresta de Selkirke, iij die Octobris.
Dns Simon Frasel habet unem equum ferrandum pomele pro corpore fuo de dono Regis.
Dns Simon de Horsbroke, miles ejufdem, habet j equum brunum badium, precii ..... xij li.

3.
year 1272
Sancti Thomae de Aquino
Inventarium rerum mobilium in castro Traiecti
dies XX mensis septembris MCCLXXII A.D.
( link http://www.corpusthomisticum.org/act.html )

"The sadelers wyffe for Diago.

Item, the xxviij.th day of Octobre, and the same yere*, my Lord payd to the sadelers wyffe of Stoke, for kepynge of Diago when he was seke

ij.s. viij.d."

* xxj. yere of the kynge

--------------------

There are a few entries in the French study on Duarte that references Portuguese and Spanish horses heading into France for a Lord.

It's not too far fetched that the horse may have been of a Spanish or Portuguese stock.

--------------------

Item een teldende part, geheten manke Trude, cofte Geryt Jach den Duvel te Delff, on X Philips scilde; hier off ontfaen V scilde, facit XI s., VIII d. groot.

= An ambling horse, named lame Trude, bought by Geryt Jach den Duvel from Delft, for 10 Philips shields (type of coin); received off this 5 shields, makes 9 s., 8 d. groot.

Een heynxt, geheten die vael Weysuyper, ende was bij na blint geworden, gegeven den tween stalmeesteren, Woutter ende Heyn Brodse; so dat men dair off hier niet en rekent ontfaen.

= A stallion; named the faded (colourwise) Weysuyper, and he had become nearly blind, given to the two stablemasters, Woutter and Heyn Brodse; so that there of, there are no receipts here.

Een pairt, heet die Coelmeeus, wort mijn heer van IJsselstein gegeven voir een heynxt, die hem mijn vrouwe sculdich was gebleven; so dat men dair off hier niet en rekent ontfaen.

= A horse, named the Coelmeeus (after the bird Koolmees, apparantly called a Great Tit in English), is being given to my lord of IJsselstein instead of a stallion, which my lady still owed him; so that there of, there are no receipts here.

--------------------