Yes, prettier jurs tend to be called flash zebras. However, Brachyplatystoma juruense has a pretty wildly varying assortment of patterns and colors, but they are still only one type of fish. Fish called flash zebras are still Brachyplatystoma juruense, but ones that people think look nice. The yellow ones and the normal looking ones can be caught side by side in the exact same waters. All jurs tend to get yellower and more boldly patterned as they get larger. The second fish posted above is representative of the "normal" juruense with boring straight stripes when it grows to adulthood.
There isn't even anything approaching a consensus in this community as to what constitutes a FZ versus a jur, because they're the exact same fish lol. When this was discussed ad nauseum a few years ago, there were many instances of person A showing an example of a normal jur, and person B would state that they felt that said fish was actually a FZ, and vice versa.
Flash zebras don't exist. They're just jurs. All of these fish are the same thing, just at different places on a spectrum of the possible. Flash zebra is a marketing ploy, plain and simple. All jurs get better patterning and coloration when they grow (note that there are never juvenile flash zebras, only gorgeous adults. Why is that?)
I intend to prove this over the next year or two.