disclaimer first: I work for a company which develops Gantt chart software. Typically, we sell our software as Gantt chart controls to other software developers so that they can enhance their scheduling applications with interactive Gantt chart functionality.
Recently, we published a free Ebook in which we provide 13 tips how to empower Gantt charts with intelligent colors. Some of the tips are also centered around the level of information you provide to the respective users. One of the tips had been published as separate blog post and deals with combining both top-down and bottom-up visual alerts. In that way, both people who need a high-level view and people who need to work on all details will get focused on the crucial tasks.