Sometimes people need to make their artwork less bright or darken.
You can do this by changing the color of individual objects, or by changing the brightness of your entire drawing. Depending on the complexity of your drawing and the final coloration you intend to achieve, the choice is up to you. Here it is shown how the colors of selected objects can be darkened or lightened as a whole. The steps are for illustrator CC 2017 version.
If you need to reduce brightness of all objects in the artwork at once please follow the instructions below.
Step 1. Select your objects. With CTRL/CMD + A short cut, you can select all objects on the workspace.
Step 2. Open the Recolor artwork dialog box. The dialog box is accessed in two ways. if objects are selected, the recolor artwork icon appears on the control panel. click this icon.
Or, go to Edit> Edit colors> recolor artwork from the pull-down menus.
Step 3. The following dialog box appears. Click the Edit tab.
Step 4. Now you should see recolor artwork panel like this:
The brightness slider placed just below the color wheel. Click preview (Recolor Art) to see the immediate result.