For those who have not taken Document Design, this page offers some introductory resources for understanding the Visual as both a practical and theoretical construct.
Gestalt
Gestalt Principles Applied in Design
Gestalt Principles for Data Visualization
CRAP
The Big Four: Contrast, Repetition, Alignment, and Proximity
Basic Design Principles: Contrast Repetition Alignment . . . Proximity
Color Theory
An Introduction to Color Theory for Web Designers
A Brief Introduction to Color Theory
Typography
A 20 Minute Intro to Typography Basics
Page Layout
Designing with Grid-Based Approach
The Secret Law of Page Harmony
Visual Hierarchy: Organizing content to follow natural eye movement patterns