Hi,

The color format option (along with some other properties like display size) is disabled for a project when a BSP has been selected. Then, the BSP determines the color format.

So if you want to change the color format to 24bit, I would recommend to clear the BSP selection for now. To do so, go to the project properties, click "Select BSP" and in the dialog click "Select none".
Then you can freely select the 24bit color format for the project.

Once you want to test your project on a target hardware, you will need to select a BSP that has 24bit as the color format selected.

Best regards,
Florian