Adjust stroke color and opacity
Paths with brush strokes have a default color (based on the color of the stroke), but you can change this color, the gradient, and the opacity. You can also make the path transparent by removing the stroke completely.
Note that when you apply a brush stroke to an object that has a fill, the object is filled first and then stroked (the stroke always appears on top of the fill).
To change the color or gradient of a stroke
Select the path or paths you want to change.
In the Properties panel, in the Appearance category, click the Stroke tab.
From the Stroke Type buttons next to the tabs, click one of the following:
None The stroke becomes transparent.
Alternatively, you can press SLASH MARK (/).
Solid color The stroke takes on the default color. You can also apply another color from the Color Picker.
Alternatively, you can press COMMA (,).
Gradient The stroke takes on the default gradient.
Alternatively, you can press PERIOD (.).
You cannot add a gradient to a bitmapped stroke.
To adjust the opacity of a stroke
When you lower an object's opacity, you increase its transparency so that you can see other objects behind it.
In the Properties panel, in the Appearance category, click the Stroke Opacity slider.
Slide the pointer up or to the right to increase the opacity or slide the pointer down or to the left to decrease the opacity. Click the slider to type a numeric value.
In the same way, you can adjust the Fill Opacity slider.
By default, the Fill and Stroke opacity sliders are linked so that changing one changes the other, too. You can click the Link/Unlink icon between the two sliders to enable them to change independently.
Some file formats do not support transparent objects and you may want to see how your design will appear without a transparent path.
To preview your design without transparency
On the Edit menu, point to Options, and then click Display.
In the Display panel, under Display options, clear the Display transparency check box.