1. The size of it, or rather the size of the hue slider. I'm working on a 24 inch 1080p monitor and I still find myself struggling to pick the right hue. It's even smaller on my laptop screen. On top of that I've noticed the way the colours are spread over the spectrum is rather uneven, which doesn't help.
Green, blue and red are largely overshadowed by shades of yellow/orange, cyan and magenta in an abrupt transition. I grabbed a ruler to see how big these specks of green, blue and red really are on-screen and we're talking about literally half a millimeter.
I put it next to the picker in Photoshop, and while Photoshop seems to do something similar with magenta, cyan and yellow instead, it's still a much smoother gradient (and nearly twice as large). This is especially obvious when you inverse the image.
2. Having to go through a dropdown menu every time time you change colour gets tedious really soon. I'd like to see some way to make the picker directly part of the UI. Possibly by making the color/gradient/image a dock with tabs rather than dropdowns.
Alternatively, and this is what I'd also love to see, access the picker with a shortcut similar to ctrl+alt+shift in Photoshop. You hold down a key and a temporary, enlarged version of the colour picker pops up right next to your cursor, until you release the key again. It's a great system for workflow and it would also at least partially solve problem 1. I've already noticed you can drag the colour picker around, but sadly it doesn't stay.
Pet peeves aside, here are some additional things that would be a bonus:
* Additional types of colour wheels/pickers such as http://i.imgur.com/ipBJfMV.png
* A small current<>after colour comparison as part of the colour picker (showing the difference between the last colour used and the current colour selected in the picker)
