I wear a lab coat when I’m working in the lab! I wear it to protect my clothes from the chemicals I’m working with. I also wear safety glasses in the lab too to protect my eyes from any chemical splashes.
(One we use is called Rhodamine which loves sticking to fat, and there is a lot of fat in the oils on your skin. Once in, it looks bright pink and doesn’t come out for days and days. Plus if it gets in clothes, it is a nightmare to get out again.)
I use the same lab coat as the one I had at school (!): dark blue, while the girls had a light blue lab coat.
Sometimes our technicians wear special clothes, like Adam describes, so that any dust and dirt (which can destroy or spoil clean surfaces) doesn’t affect the optical parts (like mirrors or lenses) that we make.