I started art lessons when I was six. The first thing I learned was that there were three primary colors, the mixture of which made up all colors. Later we were taught the color wheel, a visual representation of all color.
In astrology one starts by understanding the 12 signs of the zodiac. Later comes the art of blending relationships between the signs to create something new. How do you put together an Aries planet in aspect to a Scorpio planet? You blend them, as with color, and arrive at something unique.
The color wheel is analogous to the zodiac. Every chart has its own personal palette from which a great work of art may emerge.