Some annuals cross pollinate all the time and you never know what kind of seeds you'll end up with. It can be exciting to see what colors you get once they flower. Some flowers don't cross pollinate that easily and you end up with exactly what you had before. Annuals and Perennials are alike this way, all depending on each individual plant. I have found that if a hummingbird likes a particular flower, it really doesn't matter what color it is, other than white. This bland colorless flower rarely gets the attention of hummingbirds. They will often times skip right over the white to get to the other colors.
With Zinnias, they produce a multitude of colors and every shade within that color, and cross pollinate all the time. If I were to pick an assortment of colors, I would choose those closest to red in the spectrum, meaning reds of course, dark pinks and oranges. These are the best attracting colors and draw hummingbirds better than anything. This is not to say they don't like other colored flowers because ultimately it comes down to the quality of food within them. I'm simply saying these are the most attractive colors that will get the attention of hummingbirds. From there, they'll choose their favorites, and that's usually flavours from their past experiences.
Juvenile Ruby-throat hummingbird. August 2014, N.E. of Edmonton, Alberta.