Select more than one object with mouse in scene view

I’m using Unity 2019.4.14f1 on a Mac. In the scene view, I can select single objects with my mouse by clicking on them. I can also select a group of objects by dragging a rectangle over them. What I want to do, and can’t, is either click on several objects to select them or unselect specific objects from a group I’ve selected by dragging a rectangle over them. I want to be able to change the color of every other block in a large group of adjacent blocks. I’m fairly new to Unity and C#, so I’m not able to do this in code at this point.

Hold shift and click each one