Gradient's Renton, Wash., office space is home to 10 million sports and gaming cards, where a team of card geeks and engineers are using technology to upend a $15 billion U.S.

Using gradients, a progression of color that goes seamlessly from one shade to the next, can be an ideal way to dress up a background or add a jolt of color to a logo, avatar or other image file.

Adding a gradient to an image that starts by showing an opaque image and gradually merging the image to become transparent creates an appealing design where part of an image must be visible and part ...