That sounds awful. I did a quick search for this, and apparently Color Picker problems in FW CS4 on Lion are a "known issue". This page has a couple of official Adobe links related to Creative Suite/Lion compatibility:
Also, I found this forum posting. Have you tried using the Color Palette panel instead? Or the Color Mixer?
Thanks for your suggestions. Yes, it's possible to pick a colour through the left toolbar side panel but that still adds a couple of extra clicks to the design process which is tedious at best! I am now doing a roll back to Snow Leopard because I want to install CS 5.5 and apparently there are many more issues with Lion than just the color picker and I don't want to take any chances.!
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Very wise move because Adobe products with Mac Lion are a joke.
I cannot believe I have spend thousands of pounds on Adobe and this is how they treat us. Shocking. It's been over a year now and they still can't even be bothered to tell us whether they are going to fix their software or not.