I use Mac Paintbrush. I make a 350 width by 19 height box, and I paint the whole thing one solid color. I then use the custom color to make the color gradually become lighter, and then change to become another color entirely. That's called a gradient, and many painting apps have an auto-gradient. Finally, I insert text of what I want with the text bar, and cut/paste an image, which helps fill out space better.