When enabled, the notehead of the lowest note in the chord, the root, is always black. The color of each notehead above the root is determined by the interval between it and the one below it. For example, yellow is defined to be an interval of three semitones and green an interval of four.
If you are a complete beginner, you're probably not yet even thinking about playing chords, assuming you even know what they are. But hopefully someday you will want to play them and so you may want to consider using this color-coding option from the beginning. It's likely soon you will learn to play two-note chords and then the color-coding will appear. While you may still play these by recognizing both notes individually at first, you may begin to learn to play them based on the lower note and the color. Being able to recognize and play two-note chords allows you to build up to three-note chords, AKA triads, that combine two-note chords (as seen in the figure above). And being able to recognize and play triads is a very important skill in working towards playing proficiency.
Here is a link to a complete description of the problem of reading intervals and how color-coded chords intervals can help. If you are a beginner you may want to come back and read it after you have some playing experience, especially when you start to play two-note chords.