...is that we never really got to see the "correct" yellow ones. The red ones and blue ones are identical, aside from their colors, but the yellow ones are made of less-intricate materials and don't include collars, rank pins, or belts. Their boots were also plainer, lacking the Bajoran symbol buckles.
I think this is because they originally only made one yellow costume for Odo and specifically made that one plainer than the others to suggest his inability to perfectly copy forms when he's shape-shifting -- just like his plain humanoid face. Other security personnel early on used the backup costumes made for René Auberonois, and when they finally did make yellow uniforms for other characters, they copied the precedent that had originally been set for budgetary reasons.
I think this is because they originally only made one yellow costume for Odo and specifically made that one plainer than the others to suggest his inability to perfectly copy forms when he's shape-shifting -- just like his plain humanoid face. Other security personnel early on used the backup costumes made for René Auberonois, and when they finally did make yellow uniforms for other characters, they copied the precedent that had originally been set for budgetary reasons.