When it comes to clothing, I look for organic cotton fibers and OEKO-TEX certifications. Plant based dyes are my first pick, but low impact dyes are what most brands are using.
The standard that all companies should be striving for. Organic, wildly grown cotton and dyed with only plant based dyes. Real clothes made by real people at the source without pesticides or petroleum derived dyes. It really doesn't get cleaner than this.
*follow care instructions carefully*