Why are MLB players wearing No. 42 jerseys today?

Robinson's 42 in Dodger blue for all uniforms on April 15 - The San Diego Union-Tribune

Uniform number (Major League Baseball) - Wikipedia

Baseball Celebrates Clemente with “21” Patches; Pirates and Award Winners All Wearing #21 – SportsLogos.Net News

The Top Current MLB Player Wearing Each Number from 1 to 50, News, Scores, Highlights, Stats, and Rumors

Puerto Rican Twins don No. 21 in tribute to Roberto Clemente – Twin Cities

The only day MLB players can wear No. 42? Jackie Robinson Day

Last player to wear No. 42 for each MLB team

All of MLB to wear Jackie Robinson's No. 42 in Dodger Blue on April 15 - ESPN

Teams across MLB honor Jackie Robinson's 'eternal' impact

MLB to Celebrate Jackie Robinson Day Today – NBC Los Angeles

Remembering Jackie Robinson's historic debut 75 years later - ABC News

After Jackie Robinson, MLB integration was halting - The Washington Post

Jackie Robinson's Long Fight Against Discrimination, by Seth S. Tannenbaum, Weekend Caucus