One of the worst things about Adobe Illustrator is the fact that you can't effectively create an object with a gradient that goes from a color fading to transparency. There are so many times when you have a complex background and you'd like something to fade out, revealing that background, but there just isn't a transparency swatch that you can you use to create that type of gradient. Well, while there isn't and easy way to complete the task, not too many people know it actually can be done, it's just not as easy as it should be (you hear that Adobe). So if you've ever wondered how to create a transparent gradient in Illustrator ... here's how:
This first object represents a picture in Illustrator. Lets say you'd like to put a gradient on top of that. Here's how you'll do it.
First draw an object and fill it with the color you'd like to start with heading towards transparency.
What you'll want to do next is copy the object and paste it directly over top of your current object. This is easily accomplished by going to Edit >> Copy and then Edit >> Paste in Front.
Next, change the fill of the top Illustration to a black and white gradient. This sets the look of our transparent gradient, so just remember that the black will end up transparent and the white will be your solid color. All the Grey in between will become varying degrees of transparency.
Finally, select the two objects you created in Illustrator (the solid color object and the b/w gradient object) and open your transparency palette. From the menu in that palette, select "Make Opacity Mask" and voila, you'll see your gradient.
How it Works
The top Black and White layer acts just like a layer mask in Photoshop or Flash using the greyscale slider to achieve the varying levels of transparency. You can still edit each object independently, just click on the linked object 'layer' in the transparency palette to access that object.
So while we wait for Adobe to include the transparent option for gradients in future versions of Illustrator we can use this method to achieve the same desired result. It's just a few extra steps.