While I was working on one of my client's web site, I realised that I hadn't taken any note of the (hex) colours during my mock up phase.
Initially thinking I should download a colour picker, I realised I could probably drag and drop.
I popped open the colour selection tool in Preview (shift + apple + c), selected my colour and dropped it straight in to TextMate.
I captured it as a screencast which is just under 1Mb, created using the rather cool iShowU.