Why some sections that already i study, now are in color another again?
Why this ocurred?, sorry if my english is not perfect, i am studying it
The strength of the words you learn decreases over time. When the average strength of the words in the skill falls below a certain level (80%, more or less), the skill will not be gold anymore. You can review skills again to increase their strength back up to gold, or just leave them alone and continue to progress through the course.