For simplicity's sake, here are the answers given by Todd Hewitt in the link posted above:
Question: Speaking of the Rams color schemes, why did the Rams change from blue and yellow to blue and white in 1964, which they wore for 9 years, until 1972
Answer: Kind of a funny story. Before the change the Rams often wore yellow home jerseys which, as it turned out, didn't look particularly good on black and white TV, a consideration that became increasingly important at the time. So the Rams experimented with different shades of yellow until they found one that actually showed up well on TV. The problem was the shade of the yellow that worked well for TV was called "buttercup yellow". When Mr. Reeves (Dan Reeves, Rams owner 1941-1971) found out about this, he said that there was no way his team would ever wear a color called "buttercup yellow". Also, the yellow horns on the Rams helmet at the time didn't show up very well on TV either. So Mr. Reeves decided to remove yellow from the uniforms altogether, opting for a simple blue and white, which as it turned out looked great on black and white TV.
Question: Why did the Rams change back to blue and yellow uniforms in 1973, after wearing blue and white uniforms for 9 years (1964-1972)?
Answer: This was Mr. Rosenbloom's (Caroll Rosenbloom, Rams owner 1972-1979) idea, something he decided to do when he took over as the Rams owner in 1972. He felt the blue and white uniforms were somewhat bland and wanted a uniform look that better reflected the glitz of Hollywood. Horns were added to the jerseys, at the shoulder area, and we went to white shoes and blue shoes. The new jersey numbers were also pretty snazzy, they had a white trim. But we quickly discovered that the white trim made the numbers very tough to differentiate on TV so they were scrapped after the 1973 preseason.