I'm particular when it comes to backpacking t-shirts as I live in them and spend 70% of all my backpacking time wearing a t-shirt so it must be comfortable, soft, light and not heavy, fast drying and all the rest. And a nice color!
My current favorite is the North Face Reaxion shirts as they are very soft so I bought several and won't need to dicker with t-shirts for a long while.
https://www.thenorthface.com/shop/me...axion-amp-crew
I especially like the Citrus Yellow model and bought several.
Here's my NF shirt in action on the South Fork Citico trail on a hot day in June. This one is Chive Green.