Does placeholder text need 4.5:1 contrast? Yes, while disabled controls are exempt

The Understanding page for 1.4.3 says the criterion "applies to text in the page, including placeholder text." Measure a placeholder against the field's own background, not the page color behind the field. A #A0A0A0 placeholder on white gives 2.61:1. It fails 4.5:1. The gray #757575 gives 4.61:1 on white, and that passes. A light fill is a second test. On #F5F5F5, #757575 gives 4.23:1, and that fails, so a check on white isn't enough. For a field that might sit on white or on #F5F5F5, try #6E6E6E. It gives 5.10:1 on white and 4.68:1 on the light fill. It passes 4.5:1 on both.

The text rule has an exception for disabled controls. Its "Incidental" list says text that is "part of an inactive user interface component" has "no contrast requirement." The Understanding page adds that user interface components "not available for user interaction (e.g., a disabled control in HTML)" are not required to meet contrast requirements, so a disabled button's gray label is exempt. A control that only looks disabled but still takes clicks isn't inactive, so its label keeps the normal rule.