What is causing the discoloration on my tomato plants?

Hello everyone! I'm a seasoned gardener and I'm facing a problem with one of my seasonal vegetables. Can anyone help me with a specific question that a seasoned gardener might ask about a disease affecting one of their seasonal vegetables? I want to make sure I take the right steps to treat and prevent the disease from spreading to my other plants. Any advice or insights would be greatly appreciated. Thank you in advance for your help!