In both Aquaman’s teaser and The Flash’s teaser, the insignia themselves are made to blend in, rather than stand out.
Both Aquaman’s belt buckle and The Flash’s chest insignia are similarly brightened, giving each hero’s logo a bit more definition among the larger League.
The key difference, impossible to miss, is the bright, reflective Bat symbol taking the opposite approach from BvS‘s black variant.
That lightening is clearly intentional, but it’s merely a stylistic choice for the posters themselves (rest easy, those immediately reminded of George Clooney’s grey-and-white Batman & Robin costume).