Rui Candeias-Portuguese POW being interrogated

Good afternoon everyone. As you already know, I’ll be filling in for Andrew Lucas who, unfortunately for us, is currently unable to continue his weekly collaboration. I can only wish him the best of luck in his endeavours and a speedy return to us. I will surely miss his posts.
Before I start, I would just like to make it clear that I do not consider myself an artist and I do try to keep ‘artistic’ license to a minimum. Concerning my work and the whole process involved, I am always willing to answer any questions. Knowing that among you there are supporters as well as critics of digital colourisations, I please urge you to express your opinions, especially if you don’t agree with my interpretation. For those of you who don’t like or have no interest in colorised photos, I’ll post the original b&w in the comments.
For my first post, I chose this photo of an unknown Portuguese POW being interrogated by a German officer during the opening stages of Operation Georgette, April 1918.
On the 9th of April the Portuguese sector -11 km of front situated between Béthune and Armentières- was manned only by the under-manned Portuguese 2nd Infantry Division. After several months in the trenches and many delays, the exhausted division had finally been allowed by British Command to move off the line.
The division was in the process of packing and moving to the rear when the initial artillery barrage started. Close behind it, eight German infantry divisions from von Quast’s Sixth Army attacked along a 16 km front which included the entire Portuguese sector and parts of the British divisions on both flanks. Caught in the open and disorganized, the Portuguese offered little resistance to the German attackers.
On its right flank, the British 55th Infantry Division held the line long enough to allow for the adjacent Portuguese units to reorganize themselves the best they could, and together with British elements, start resisting the German advance, but on the left flank, the hard-pressed British 40th Infantry Division made a hasty strategic retreat leaving the Portuguese flank wide open. An opportunity the Germans quickly explored with a flanking manoeuvre that cut the Portuguese retreat. This situation later caused severe attrition to Portuguese-British relations with, as we say in Portugal, “the blame dying single” as both sides blamed the other for the defeat.
Portuguese losses during the operation were: 1314 KIA, 4626 WIA, 1932 MIA, and 7440 POW. Representing 2 thirds of the division, most of these losses were suffered during the initial hours of the offensive.
Concerning this particular photo:
The German officer, whom the IWM caption describes as belonging to Intelligence is, according to his tunic, from an Ulan unit. The colour of his cap’s band and piping was most probably white. The only other possibility is cornflower blue which would show as almost white. From what I understand, only 5 regiments matched these colours.
If white:
2. Pommersches Ulanen-Regt. Nr.9
Königs-Ulanen-Regt. (1. Hannoversches) Nr.13 (Hannover)
Kgl. Sächs.1. Ulanen-Regt. Kaiser Franz Josef von Österreich, König von Ungarn” Nr.17
If cornflower blue:
Lithauisches Ulanen-Regt. Nr.12
Ulanen-Regt. Hennigs von Treffenfeld Nr.16
From what I was able to find, of these five regiments only three were, or had elements, on the western front in April of 1918: 2. Pommersches Ulanen-Regt. Nr.9, Königs-Ulanen-Regt. (1. Hannoversches) Nr.13 and Ulanen-Regt. Hennigs von Treffenfeld Nr.16.
None of these units seems to have been stationed close to the Portuguese sector or Fourmies Prison Camp where according to the IWM caption (for all its worth) this photo was taken.
There was a significant community of German citizens living in Portugal before the war, many of which returned to Germany after 1914, some to serve in the armed forces. Maybe this man was one of them and, being able to speak Portuguese, was detailed to interrogate POWs. At present, I can only speculate so I chose white for demonstration purposes only.
Original: IWM (Q 55260).