Background to my web/app - tool


#1

It’s not a typical UX/UI question, but maybe someone would be able to help me.
I want to work on some UI hi-fi prototypes in my free time and I am wondering what tools I can use to create / paint a background to my landing page / app. I want to create something like this:
https://t2.genius.com/unsafe/300x300/https%3A%2F%2Fimages.genius.com%2F41d606e3a11c18efaf3e49725bde0449.640x640x1.jpg

If you know any software that I can use, I would be grateful for any tips! Cheers!