One of the more-popular Dock modification hints in OS X 10.5 enabled a Stack target highlight on mouseover. With that hint in place in 10.5, when you moused over an item in a Stack in grid view, the item would highlight, making it very easy to see. The hint only worked for grid view, and had no impact in fan view. (List view already has a highlight on mouseover.)
With the release of 10.6, though, that hint broke…or so it seemed at first glance. In reality, Snow Leopard actually improves on this feature, and now offers two different ways to invoke it. You can either permanently enable it via a Terminal command, or use it on an as-needed basis.
To use mouseover highlights on an as-needed basis, you just need to change how you activate your Stacks. Instead of clicking on your Stack and then immediately moving the mouse into the Stack area, click-and-hold on the Stack icon until your Stack appears. Now when you move into the (grid or fan view) Stack, you’ll see a mouseover highlight effect (a blue background in fan view; a silver one in grid view).
If you’d prefer to have the mouseover highlight appear even on a simple click, it turns out the hint from 10.5 still works—except Apple corrected a typo in the hidden command! To enable mouseover Stack highlights in Snow Leopard, open Terminal (in Applications -> Utilities), and enter these two commands:
defaults write com.apple.dock mouse-over-hilite-stack -boolean TRUE killall Dock
(In 10.5, the name of the command had a typo in it; it was
mouse-over-hilte-stack.) When the Dock relaunches, you’ll see that you get the mouseover effect, in both grid and fan views, after simply clicking a Stack. If you decide you prefer the default behavior, use these two commands in Terminal to return things to the way they were:
defaults delete com.apple.dock mouse-over-hilite-stack killall Dock
Personally, I like the always-working mouseover effect, so I’ve left this hint enabled on my Snow Leopard machines.