Making a custom brush in Illustrator can be easy and frustrating at the same time. No matter which type of brush you create, one of the most important settings to pay attention to is the ‘colorization method.' If you don't change the colorization method from the default setting, you won't be able to customize the colors of your (custom) brush strokes later. Here's what you need to do…
This tip requires basic knowledge of Illustrator, the Illustrator Brushes palette, and creating a custom brush in Illustrator.
So you have your artwork selected and select “New Brush” in the brush palette options (like above). Now you have the option to choose which type of brush to create (below). I'll use “Art Brush” in this example.
Make sure you select “Tints” (what I personally recommend) or “Tints and shades” as the ‘Colorization Method' before you save your new brush. If you don't, all of your brush strokes will be black, (or the color of your brush when you created it). There are workarounds like expanding the appearance of your brush stroke, then changing the color, but if you do happen to save your brush and accidentally skip this setting, all you have to do is double click on the brush in the Brushes Palette to bring the options panel up and change the options.
This drove me nuts for the longest time, back when I first started experimenting with making custom Illy brushes. I recommend experimenting with custom brushes for 2 reasons: 1. It never hurts to learn more, and 2. Brushes (especially vector) can save you tons of time, if you only take the time to make them. However, it might take a while (experimenting) to learn how it all works in order to make brushes at your leisure and get the desired results regularly.