Quiktip- Control the Opacity of Individual Colors In Illustrator
You can easily control the opacity of colors in Illustrator. You can Control the opacity of the stroke and the fill individually by using the appearance panel. Directly under each stroke and fill layer in the appearance panel, there is an opacity section, where you can set the opacity for one element, and you could leave it alone, or make it less or more for another. This means that you could have a 100% black stroke, with a 50% fill.