A polyester DTY fabric may look uniform in greige form, then develop visible barré, streaks, or shade differences after dyeing. The frustrating part is that the dye bath is not always the real source of the problem.
A yarn label such as 75D/36F can look simple until you need to compare two materials or predict how they may behave in fabric. So, what does 75D/36F mean? It identifies a filament yarn with a total linear density of 75 denier made from 36 individual filaments.
Two polyester fabrics can look equally vibrant at first yet age very differently under sunlight, washing, and repeated use. The reason often comes down to when color enters the material.