I have a colleague who has recently dyed his hair to be darker and not quite as light and gray. I think it looks really good and I would like to comment on it, but I am not quite sure how to approach it. If I say "Hey, your hair color looks great!", it brings attention to the fact that I was aware of what his hair looked like and that I noticed how drastic of a change it is. Perhaps he thought it was just a very subtle touch up and it would not be a big change, but now his colleagues are aware that he dyes his hair.
How can I comment on a coworker's change to their appearance (whether it is teeth whitening, hair coloring, tanning, etc.) while being sensitive to whether or not they meant it to be a drastic change or just a very minor change that only they would notice?