The default behavior in vPlanner is that the task colors will be based on the colors assigned to the user's company. You can change this to use the Discipline colors if the user is associated with a discipline or the Category color if you had configured the colors for the task categories.
The options in this section control how milestones are displayed. If the Override milestone color is enabled, then all milestones will be displayed using this color. Otherwise, the Color-By setting will be used.