There's a colour picker tool next to the Fill and Outline (and glows and many other layer style features etc) in the Timeline of After Effects.
However I've never found a reliable way to Select and activate it.
Sometimes a double click is required, sometimes a triple click, and yet other times it will magically be selectable the first time.
It seems to make no difference what the current selection is. It's just incredibly unreliable/difficult to activate this tool/feature.
Anyone else have this problem and/or know of why/how to make it reliably pickable?