Hi, I will try answer this in respect to the Merowingian military. (6th-8th century)

The most important question to ask is, if those troops were standing troops (like the roman troops) or if they were farmers that got called to arms when they were needed. Research points more to the latter. Even though the roman heritage especially in the southern parts of Gaul was very strong indeed, it is very unlikely that there still existed a standing army. There are historians (Goffart, partially also Bachrach) who are arguing in favor of a standing army, but modern research does not point in that direction (compare Halsall, Petersen, Sarti). It is clear that the core of the army was made up of so called 'farmer-soldiers' and if the king called for troops, able men were levied (who and how many were levied was dependent on multiple factors, for example wealth). Gregory of Tours, the most important chonicler of that time, does write how men of his church had to pay 'bannum', which was a fine, because they did not appear to serve their military service. (Hist. 5,26) Also in another passage, Gregor describes the 'minor populus', the simple people, the same term he uses to describe the civilian population at other passages, as the heart of the army, so he does not appear to describe professional soldiers. (Hist. 4,31)

So this accounts for most of the men at arms. But there were special cases. It is very likely that the descendants of the roman soldiers that served in Gaul did preserve their military tradition at least for some time. Procopius, an eastern-roman writer, for example writes about soldiers under frankish command who still wore the same armor as they did under imperial command. Bachrach considers this account to be at least a bit trustworthy, as armor was very expensive and it wouldn't be unusual to have armor in use for multiple decades or more. But even here we can not be sure, if there was any uniformity aside wearing partially the same kind of armament.

Also, consider that a uniform usually makes you part of a kind of instituition/organisation. The army as an institution did not really exist anymore in merowingian times. The civil and military government were fused together. For example the 'comites', the counts, did have a civilian function as well as a military one. The terminology points in the same direction. In roman times a soldier was a 'miles', but in merowingian times the usual terms we read are 'armiger' (someone who wears armament), 'belliger'/'bellator' (someone who does war) or simply 'viri fortes' (strong men) or 'pueri' (boys). While the roman term 'miles' was an identification with an institution, the merowingian terms describe what makes these men different from others.

The warriors that were levied usually had to bring their own armament, which makes it very unlikely that they would have been uniform, but in the end we can only speculate. Especially not as much as in the pictures you have linked (But I can not speak for english military, even though I doubt uniformity there was higher than in Gaul).

If you want to read up on this:

Sarti, Laury: Perceiving War and the Military in Early Christian Gaul.

Petersen, Leif Inge Ree: Siege Warfare and Military Organization in the Successor States (400-800 AD). Byzantium, the West and Islam.

Bachrach, Bernard S.: Merovingian Military Organization, 481-751.

Bachrach, Bernard S.: Grand Strategy in the Germanic Kingdoms: Recrutment of the Rank and File, in: Kazanski, Michel/Vallet, Francois (Hg.): L’arm´ee romaine et les barbares du IIIe au VIIe siecle.

Bachrach, Bernard S.: Procopius and the Chronology of Clovis’s Reign.

Halsall, Guy: Warfare and Society in the Barbarian West, 450-900,.