As nobody has come up with an answer and I don't like unsolved mysteries, I've done some research of my own.
For anybody interested, there's a good website here
http://www.spanishsuccession.nl/ with detailed information. I take the following account from their site (
http://www.spanishsuccession.nl/armies_ ... antry.html) with some rearrangement of the content for chronological reasons and omitting the footnotes:
"In early October 1701 the Amenzaga tercio left Oostende for Brussel. On sunday 9th it was revued there by Prince Tserclaes. On 22 October 1701 the Amenzaga Tercio was to leave Brussel for Upper Gelre, but was later destined to Gent, where it had arrived on 2 November 1701. The Amezaga regiment was in Gent in April 1702 its colonel was Juan Antonio Hurtado de Amezaga. During the August 1702 attacks in States Flanders the Amenzaga suffered heavy losses. On 17 June 1703 the Amezaga was destined for Bedmar's army. On 30 June 1703 the Amezaga regiment fought in the battle of Ekeren. On 4 August 1703 it received orders to leave its camp at Duren and to join the main army101d. On 3 november 1703 the Amenzaga was stated to have arrived in Gent.
The Los Rios regiment then appears in a 12 May 1705 order of battle. In the Battle for the Brabant lines the Los Rios was part of the Zuñiga brigade that defended the part that the alliance attacked. In this battle these officers of the Los Rios were taken prisoner: Captain Aranda; Lieutenant d'Aquilera and ensign Mena. From 5th June 1706 there is a note in the Oprechte Haerlemsche Courant [https://www.delpher.nl/nl/kranten/view?coll=ddd&identifier=ddd:011105816:mpeg21:p002] that on 2 June 1706 the '
Los Rios, previously Amenzaga, that defended the citadel of Gent surrendered to the alliance and was made prisoners of war'. It was then stated to count 400 men. In a letter to the States General the Duke of Marlborough stated: 'The Spanish battalion consisting of 400 men, with the colonel, the Marquis de Los Rios, and all the officers being made prisoners of war, but all the soldiers, except 50, declar'd for King Charles.
I did find that on 1 February 1707 a 'Spanish' Los Rios regiment passed to French pay and in 1710 it took the name 'Las Sierras' and in 1711 the name Leon. In another source we find that the regiment 'Galicia' was conducted to Spain under the command of 'Sierra' in 1715 and that he was its twenty-sixth colonel. It continues with stating that he was succeeded by Don Juan de Leon and Don Pedro de Castro and that in 1715 it got the name Galicia. It's thus established that the Los Rios regiment later became the Galicia regiment, and we only have to know which of the Spanish regiments later became the Galicia. According to Juan L. Sanchez the Galicia regiment was commanded by Amezaga in 1702."
So it seems as if the Los Rios regiment may have split after being taken prisoner at Gent in 1706 with part of the soldiers entering Allied service and was later merged with Bournonville and continued as 'Los Rios' in Imperial service, while another part - perhaps under the original commander - continued to serve on the Franco-Spanish side.
There's a plate depicting the uniforms of the Tercios and Regiments located in Flanders that I found on
http://www.oocities.org/ao1617/weapon.html sometime ago. The plate shows the "Tercio de Amezaga" with grey-white uniforms and red cuffs, which conforms with the uniform of the regiment up to 1744 (
http://www.kronoskaf.com/syw/index.php? ... s_Infantry.)
So sadly, probably no green uniform here.