If, like me, you were wondering why the excellent Pixelmator got out of the door without an easy way to see the colours you’ve picked in HTML-friendly hexidecimal form, the way you can in Photoshop - well, it’s actually that OS X has an altogether more elegant way of handling this kind of thing.
I didn’t know this, but the colour picker widget shown in PixelMator is a standard OS X one, and you can plug in new widgets for it. One such plugin is the Hex Colour Picker. Once installed, PixelMator picks it up as a new toolbar button on the colour picker widget (as will every other app using this widget) and you can copy the HTML-friendly colour from there. Simple, but very effective.