From Livescience.com:
" But barns weren't originally red in fact, they weren't painted at all. The early farmers that settled in New England didn't have much extra money to spend on paint , so most of their barns remained unpainted. By the late 1700s, farmers looking to shield their barns' wood from the elements began experimenting with ways to make their own protective paint.

A recipe consisting of skimmed milk, lime and red iron oxide created a rusty-colored mixture that became popular among farmers because it was cheap to make and lasted for years. Farmers were able to easily obtain iron oxide the compound that lends natural red clay its coppery color from soil. Linseed oil derived from flax plants was also used to seal bare wood against rotting, and it stained the wood a dark coral hue."

I noticed a number of my photos show circular structures near the barn. This particular one drew my attention because it had the name Butler painted on the side. Curiosity got the better of me and I went to see what Google might yield. It turns out Butler is a long-standing manufacturer of grain storage and other structures (like, now, even airplane hangars) headquartered in Kansas City and operating in many countries. I found they have a regional representative not 20 miles from where I photographed this early (?) example of their work.

I wonder if the bins in lhammer43's photo from S Dakota (p.4) are Butlers? Oh yes! I see the name on the one on the right. Now I shall watch out for Butler bins!

Butler's rise is a truly remarkable story of what American entrepreneurship can accomplish when challenged. The audacity of the government's challenge is remarkable too. I think this piece from their web site will bear repetition - almost unbelievable:

"Butler Manufacturing Company introduced its first galvanized steel grain bin in 1907. By 1938, research had proven the superiority of these bins over wooden ones, and the next year, the U.S. Department of Agriculture announced its intention to receive bids on delivering 30,666 steel bins needed to store excess grain from a bumper crop. This order was one and a half times more bins than had been produced the previous year by the entire industry. Guaranteed bids had to be submitted within 30 days and delivered within just 60 days of receiving an order. Butler took on the challenge and, against phenomenal odds, refurbished an abandoned plant in Galesburg, Illinois, supplied it with machinery, staffed it, and mass-produced 14,500 steel bins in 59 days, plus another 6,000 bins in just 15 days. The seemingly unachievable became achievable through Norquist's clear vision, the company's adventurous commitment, and the efforts of hundreds of motivated people. The event was a spark that began to shape what Butler Manufacturing is today."

This clip comes from the page illustrated in the last image.
https://www.butlermfg.com/about/