This article explains the colours on the Planned v Actual Chart

Stage Headers will be mid blue with a dark blue bar showing the progress of the Stage.

Tasks are grey and will remain grey once they are activated.  The dark blue bar will progress across the task until it is complete.

Milestone Task will show as yellow bars.

A task on critical path is depicted by a dark blue border and the bar will have rounded corners.

The dark grey lines show the tasks original planned times.

Grey Diamonds are tasks which have zero duration.