Open palete of the color picker.
Move mouse over any color square (over any color).
You see a blue shadow of the focus.
If you move mouse over the neighbor square, you could note, that blue focus border consumes mouse move events too.

Shadow is so big, that it overlaps with the center of the neighbor square, which makes our tests sometimes to move cursor on the border, and not into the center of the neighbor square.

RULE ControlsAutomatedTestSuite/javafx/scene/control/test/colorpicker/ColorPickerTest/keyboardArrowHorizontalNavigationInPopupTest Exception Expexted: selected color: ...; focused color: ...