Making a watercolor effect in Illustrator is easy.
First, create a new file with the desired size. You can use any size you like, but for this tutorial, I’ll use a 600 x 800 px file.
Next, open the file in Illustrator and create a new layer. Use the Rectangle Tool (M) to create a rectangle that is the same size as the file. You can hide the first (artwork) layer file to start working on your rectangle without distraction.
With the rectangle still selected, go to the Effect menu and choose Stylize > Watercolor. This will open the Watercolor Effect dialog box. But first, let’s add some color to our rectangle. You can use the fill & gradient tool to do so. In this example, I used a freeform gradient. Then, go to the Effect menu and find the Watercolor effect. If not in the Stylize menu, then it should be in the Artistic section. Set your Watercolor effect in the dialog box then click Ok to proceed to the blending process.
First, set the Mode to Overlay. This will allow the colors in the rectangle to show through the watercolor effects. Next, set the Opacity to 100%. This will make the rectangle completely transparent, and the watercolor effects will show through. You can unhide your first (artwork) layer to see the difference it makes.
Finally, set the Blending Mode to Lighten. This will allow the colors in the rectangle to blend with the watercolor effects.
Now, click OK to close the Watercolor Effect dialog box.
Your rectangle will now have a watercolor effect, and the colors will blend together nicely.
Making a watercolor effect in Illustrator is easy. All you need is a layer and the Stylize > Watercolor effect, and you’re good to go.