Your first choice is finding the right color scheme and style that compliments the room. If you have a modern contemporary style, you may want to stick with just two or three colors at the most. These colors are picked up somewhere else in the room - a picture, or the bedding, for example. Contemporary style allows geometric designed pillows and straight lines along with solid colored pillows.
Country style allows for much more liberty in design choices. You
will see floral designed pillows as well as solid colors. Country décor allows for affluence in the number of pillows as well. You could say “busy” would fit readily here. This style allows for a mixture of different styles. You may have an antique style bed and a modern dresser for example. This style encourages flexibility.
Victorian style is a formal vintage style. Frills, tassels and lace are appropriate as an accent and compliment the solid colored pillows.
Pictorial accent pillows work as well. Carved furniture and ornate detailed accessories fit perfectly here. The color scheme could embrace the darker colored walls with a mix of delicate floral pastels in your pillows and other accessories.
In all the choices of style and colors, one thing is predominant. What you enjoy is top priority. You are the one who lives with it, so the colors and style you choose should make you feel good. Your choice in colors for the decorator pillows should best be what is found somewhere else in the room. This will tie your room together to complete your theme and create the atmosphere you desire.