It's the little things that matter in campaign fundraising. And sometimes hugely.

A Republican National Committee analysis of five months of fundraising during the 2016 presidential campaign found that positive images and words and cool colors did well, while photos of President Trump's rival, Hillary Clinton, chased donors away.

The "RNC Testing Booklet," newly highlighted by the campaign training group American Majority, found that two tweaks to emails and literature changed the game between the Republican National Convention and Election Day.

A big driver for higher donations was a simple green "contribute" button. Typically, they are red or blue, but introducing green proved a boon. In one case, donations increased more than 38 percent when a green button was tested against blue and red, a color commonly used to give a sense of urgency.

Another plus was using photos of Trump flashing his trademark thumbs-up. Those pictures, when tested against others, resulted in thousands more donations and bigger checks.

"We found that the thumbs-up image continued to be more effective," the RNC said.

American Majority, based in Purcellville, Va., urged new candidates to copy Trump: "This was a theme for the RNC last year – thumbs-up pictures of Trump were the most effective. In some cases, it increased per-visit revenue by 30 cents to 40 cents over other images! The next time you send your donors to a splash page for donating or signing up, try using an image of the candidate with their thumbs up — and definitely smiling! Maybe your candidate has a different 'signature look.' Use images that make your candidate look the most appealing and positive to a website visitor."

Somewhat surprisingly, using an image of Clinton did not scare Republicans into donating. The RNC tested a fundraiser using a black-and-white image of Clinton and one of Trump with his hand over his heart.

The result: "We tested background images of both Hillary Clinton and Donald Trump on the 'Follow the Money' donation page. The Hillary Clinton image was an immediate drag on revenue, with donations almost 2-to-1 in favor of the image of Donald Trump."

And the president's current theme of "Drain the Swamp" took time to settle in on GOP campaign literature and email.

"We tested four different calls-to-action for the header text of the donation panel on the We Won The Debate page after the national debate," the RNC said. "The test ran from October 20-22 and compared 'Drain The Swamp,' 'I'm With You,' 'Thank You' and 'Win Back America.' Initially 'Drain The Swamp' and 'I'm With You' were ineffective and traffic was filtered off; however, 'Thank You' was time-sensitive and had to be removed from the test, so 'Drain The Swamp' and 'I'm With You' were added back in. From this point on, 'Drain the Swamp' was the most effective of the three remaining options."

Paul Bedard, the Washington Examiner's "Washington Secrets" columnist, can be contacted at pbedard@washingtonexaminer.com