Gradual color change background in poster

Quick answer：

A gradual color change in a poster's background refers to the transition from one color to another across the background. This technique can be used to create visual interest and draw the viewer's attention. Designers often use gradients or color blending to achieve this effect. It can be done through software like Adobe Photoshop or Illustrator, where various tools are available to create smooth and seamless transitions between colors.