OK, I understand. Take a look at the "Create a new type of Gantt bar" section of the following Help article:

Format the bar chart of a Gantt Chart view - Microsoft Support

Create a custom task Flag field and give it a name of your choice. Insert this Flag field in any Task view and set a Yes value for tasks where you want a different Gantt bar color automatically. Then refer to the steps in the Help article to make this work. For example, I just automatically formatted a Gantt bar color using the dark Orange color when I entered a Yes value in the Flag1 field for a task, so I know this approach will work for you. Hope this helps.