Does anyone know why? I don’t actually know for a fact that this is true, but it does appear to me that yellow is far and away the most common color in wildflowers, in the western US.
If they in fact are the most common, I’d guess that bees are more attracted to them than other colors, resulting in more pollination.
Objectively most flowers on wild herbs are insignificant green, pale yellow or white things. They aren’t very noticeable so you don’t see them. So what you have left in your sample are the larger, showy flowers that you notice.
But for large showy flowers you’re quite correct, yellow does usually dominate in open environments.
Flowers only have the chemicals to produce red and brown pigment, just like humans. Blue colours have to be manufactured by some tricky refraction processes, which is why blue is relatively rare. Red flowers tend to be uncommon anywhere because bees can’t distinguish between red and green. White flowers are similarly selected against because they have no colour at all.
So in our sample we’ve removed the greens and whites, we’ve removed the reds and we’ve removed most of the the blues.
So that really only leaves the yellow- orange spectrum. And what constitutes yellow and what orange is arbitrary anyway. IOW the odds are highly in favour of yellows in any sample of field flowers.
However that doesn’t apply to other environments. Forest floor flowers tend to have more blues and whites, because red-based pigments look dull in the filtered light of a forest. Flowers pollinated by birds over-represent red and white because the vertebrate eye can see those most clearly. Night pollinated flowers tend to be white because that is the most luminous in low light conditions.
But for flowers growing in full sunlight and pollinated by bees yellows will predominate.
This is not quite true, some plants have true blue pigments (e.g. Anthocyanins), many of them colored complexes that turn from pink/red to blue depending on pH (acidity), resulting in shades of lilac, violet and purple (cite, cite)
Good catch. The embarassing part is that I knew that, somewhere in my ancient and increasingly unreliable memory. :insert blowjob smiley:
I just wanted to say that Blake is right, on whitish being the most common, followed by yellow, then red, then blue. There are a few botanical families that have many blue flowers, but there far, far more families that have only whitish or yellowish flowers.
Also, I wanted to link to a holiday photo I made in Spain this spring. It’s a field of three different yellow-flowering weeds. Rather beautiful and fitting to the OP.
I’m sorry it has taken me so long to get back to this thread - first I was traveling (looking at roadside wildflowers) then I was ill and couldn’t do any posting that required thought. 
Anyway, thank you for the responses and I have another question - can someone point me towards a good book or website that will identify these wildflowers for me? I am mostly in California, Arizona, Utah, Idaho and Montana.
Wow, you must be HUGE!
I’m not in all those places at the same time, silly! Tho, yes, I am overweight - sigh
In California, at least, some highly invasive plants happen to have yellow flowers. (Broom? Mustard? I can’t remember which it is that you see everywhere.) Here in San Diego we also have some yellow daisy-like thing that was purposely planted because people thought it was prettier than the native coastal plants and it’s been hard to get rid of in places they are trying to restore.
So if I took a bunch of violets or bluebells and powdered them, I wouldn’t have blue powder? I knew that was true of blue bird feathers, but not of flowers.
I think it is mostly mustard that we have huge fields of in the spring.