So may I present: Argyle Scribble! This is created in Illustrator. Be sure to keep the Appearance panel open, as that's how you'll target the different fills. Illustrator always adds new fills to the top of the stacking order, so we'll be working from the bottom up.
This is what we'll be making: (click on the photos to enlarge).
Note: The top photo looks slightly different than the one below it. To get that effect, use the default red-orange gradient instead of pink in step 3.
Step 1: Make a rectangle with a summery gradient fill.
Step 2: Add a Teal fill, some scribble, and adjust the blending mode.
If you don't like the rough edges, you can simply add a thick white stroke, and move the stroke to the top of the stacking order in the Appearance Panel be sure to make the stroke visible.
Step 1: Make a rectangle with a summery gradient fill.
Step 2: Add a Teal fill, some scribble, and adjust the blending mode.
Step 3: Add a pink fill, add some scribble (using the negative value of what you used for the teal scribble), and adjust blending mode to your liking.
Step 4: Add a white fill with some thinner scribble.
Step 5: Add another white scribble fill, but flip the angle of the scribble.
Interestingly, you can also apply pattern swatches to the scribble fills and it gived it kind of a grunge effect. Here are a few interesting ones I came up with.
So you don't have to recreate these every time you want to use your special argyle scribble design, drag your completed object into the Graphic Styles panel to save it as a graphic style.