The changecolor app will allow you to change the colors of all entities/objects in a drawing.
You can change a color from BYLAYER, BYBLOCK and vice versa.
It is also possible to change the colors of entities inside the blocks in the drawing.
You can use custom script or script routine to change the color of the entities.
For more details please refer Index.html from the installation folder "%PROGRAMDATA%\Autodesk\ApplicationPlugins\hap ChangeColor.bundle" to get started.