You're experience of your first day back at work literally mirrors mine. I also had thinning hair loaded with concealers so it wasn't a stark change. The comments I got were all similar to yours "your new style suits you" etc. like yours the colour was slightly off but nobody noticed and all I got were positive comments. Once you've seen everybody once (friends, family, colleagues etc) you can tick that box of transitioning between consealers and system and get on with focusing on how to make it look the way you want it to.