What is it with August and yellow flowers? Last week Pete and I revisited the Yampa River Botanic Park in Steamboat Springs. As I expected, the gardens were in full bloom—dazzling in the clear mountain sunshine. As I strolled the pathways, I noticed expanses of Coreopsis, clumps of Rudbeckia, beds of sulfur-yellow buckwheat (Eriogonum), and sprays of goldenrod. And that’s when I realized that the majority of blooms were in some shade of yellow.

Sure, there were purple flowers too—salvias and lavenders, hardy geraniums and purple coneflowers—but the cool purples simply set off the yellows, making them even more noticeable.

The next day, as we drove home across the Rockies, I realized that the garden had simply imitated nature. Yellow rabbitbrush lined the highway in the higher altitudes, then was joined by mile after mile of black-eyed Susans dancing in the breeze.

If Mother Nature has a favorite flowers color, it has to be yellow. What is it about that color that makes it so popular? It turns out that insects—including bees and other pollinators—can’t see the same colors we do. For example, they see yellow and blue/purple the best. Red looks black to them, but in compensation, insects can see further into the ultraviolet end of the spectrum than us humans.  As a result, flowers that are pollinated by insects tend to be yellow or purple.

Of course, we gardeners aren’t content with flowers—such as zinnias—in only a limited palette. We mess around breeding blossoms in colors which nature would never have considered. And now we have cultivars such as ‘Moulin Rouge,’ a pinkish maroon sunflowers. Petunias were originally a lavender purple, but now they come in every color but blue, including black! Zinnia elegans started out with purple petals, and now they too come in a crayon box array of hues.

Being red (or brown, or even black) isn’t a disaster for a flower. Bees are also attracted to scent, and may approach a red flower if it smells right. Hummingbirds and other birds are partial to red flowers, so many species that are naturally red have also adapted their shapes to cater to the birds’ preferences. And there are other pollinators—flies, lizards, moths and butterflies—which have their own favorite colors.

Still, with so many yellow flowers in bloom, especially at this time of year, it’s clear that yellow equals success.

We may become a bit jaded by all the yellow, but if we could only see as a bee sees, we’d realize that yellow is just the beginning. Flowers advertise in the ultraviolet, too. What looks like a solid color to our eyes may be decorated with stripes, splotches, and other markings all designed to lead a pollinating insect to the center of the flower. Dandelions and evening primroses, for example, both have dark centers. The latter adds thin stripes arrayed like spokes around the middle blotch, ushering the bees inward.

While I can’t take UV photos, try doing an image search for “flowers ultraviolet markings” and prepare to be amazed. Then click over to post by National Geographic, “Pictures Capture the Invisible Glow of Flowers,” for a look at Craig Burrows’ phenomenal photography.