Drupal 8 Block Plugin API: How to create a custom block in drupal 8
Theme Inheritance: Creating a Drupal 8 sub-theme, or sub-theme of sub-theme

Problem:

Changing theme colors using the admin area failed.

Solution:

The logo.png file was missing from the theme's root folder, probably causing a uncaught exception that caused the bug. After locating the image file in thr correct place (root folder), the problem ceased.

Pre-defined color schemes

Pre-defined color schemes are declared in 'color.inc' file, as an array inside 'schemes' array, and are executed in 'preview.js'. So we can use these 2 files to add color definitions to the theme.

45 Modules in 45 Minutes
by Rod Martin, Director of Training at Open Source Training

The Code Filter module provides an easy method to integrate code snippet in node content.
It displays the code in a distinct form, and with no need to handle special characters.
See more information in Daily Dose of Drupal Episode 44

Need: I have a content type with a File field. When this field is displayed, I want it to show only icon without any text.
The current formats are either "Generic file" (icon + file name), "Table of files" (icon + file name + size) and "URL to file" (the entire file's URL).
I want to add a format "File icon", that will display an icon that utilizes as a link to the file.

What I did:
I created a very simple module called "File icon". I placed the file_icon directory in sites\default\modules