Yes, zellige-effect tiles are meant to look uneven. Zellige-effect tiles are designed to recreate the look of handmade Moroccan tiles. Expect each tile to differ in shade, surface and glaze depth. Edges can be slightly irregular, and some tiles may have small chips, pits or bubbles in the glaze. That variation is what gives a zellige wall its character, so it isn't treated as a fault.
To get the best result, open several boxes and mix the tiles as you lay them so the variation is spread evenly across the wall. If a tile has a defect you don't like, use it for cuts.