It all depends on personal taste. The biggest mistake that people tend to make is to plant too few bulbs. Then they're disappointed come spring. One of the reasons is that, in fall, there is still summer color in the garden. Mass tulips together.
Color is an important aspect of art and of life.
Color in the garden, especially in the spring garden after the long, dull winter, has the added vibrancy of being true living color. Colors that might otherwise clash, often look surprisingly good together in a garden setting. What's most important to remember is that fall is the time to think of spring color. Perhaps a comment from Connie Cross sums it up best. When that first tulip or daffodil blooms in the garden, with nothing else around, it's worth a million dollars.