These settings work for several Blue Pencil tools
To adjust Blue Pencil stroke size
Press B on the keyboard while dragging left or right in the Viewport. You can also right-click the tool icon in the Blue Pencil Toolbar to view the settings specific to the tool.
To adjust Blue Pencil tool opacity
Press M on the keyboard while dragging left or right in the Viewport. You can also right-click the tool icon in the Blue Pencil Toolbar to view the settings specific to the tool.
To change brush color