Here is a vector of abstract colorful rainbow art form thevectorart.com, scalable Illustrator format. This means they’re fully scalable, available to use for print or any other digital medium.

Name: Abstract Colorful Rainbow Vector Art
Homepage: Vector Art
License: Creative Commons Attribution 3.0
File Type: EPS
This image is a scalable vector graphic and can be scaled to any size without loss of resolution. This image will download as a .eps or ai file. You will need a vector editor to use this file (such as Adobe Illustrator or CorelDRAW).