The red line indicating you are out of range for a particular skill needs to be moved to the top of the skill buttons, as the hotkey indicator hides this bar a little bit, especially when in combat when you only have time to glance down quickly. This is especially true on toolbelt skills which are smaller and harder to see at a glance.
It would be nice to also thicken the red line, or get rid of it and just dim the skill buttons that are out of range.