"Tangier, England's lost Atlantic outpost, 1661-1684" by Routh
page 185
Apparently, they were from Catalan. No mention of uniforms that I can see.
"a treaty between England and Spain was signed at Windsor by
the Spanish Ambassador, Don Pedro de Ronquillos. In
view of the pressing need of cavalry at Tangier, and the
difficulty of transport from England, the King of Spain
gave orders for two hundred Catalan horse to be put at
Colonel Fairborne’s disposal; it was also arranged that
horses might be bought in Spain for the use of the Tangier troopers.
The Governor of Andalusia was requested to send the
Spanish troops to “a place they call Barbatt and Bologna
Bay,” which Herbert reported to be the most convenient
point of embarkation. The Admiral sent ships over for
their transport, and they arrived at Tangier just in time
to do gallant service in a victory over the Moors won at
the end of October."
They are mentioned a few times after that, search the text for 'Spanish.'