Class 2 Hi Vis Tee, Short Sleeve, Yellow
Yellow, short sleeved and built to be seen: a class 2 hi vis tee for warm-weather work.
Class 2 covers a lot of ordinary site requirements, and having it in a tee rather than a vest means one garment instead of two. It moves the way a shirt should, it does not sit over the top of everything trapping heat, and there is nothing to catch when you reach. The yellow is doing the work here, and the reason to keep it clean is not appearance but function.
Wear it alone in summer and under an open jacket in the shoulder seasons where the colour still shows. These are worth owning in quantity, because visibility clothing that has been worn three days running has stopped being visibility clothing. Take your usual size, or one up if you like room at the shoulders.