1 Colour theory
See colour.
2 EZ-design tools
Instant logo design: Hatchful.
Canva semi-automated web-based graphic design for basic stuff (certificates, posters, cards).
Figma also semi-automated web design with lots of collaborative widget thingies.
3 For diagrams
Maybe see diagrams.
4 Applied to web
See website cheats.
5 UX theory
See user experience.
6 Images
See image editing.
7 Recreational theory of
See weaponized design.