Use --placeholder-color instead of --background-color for placeholder-* utilities (#19843)

This PR fixes an issue where `placeholder-*` utilities were reading
values from `--background-color` instead of `--placeholder-color`. In
Tailwind CSS v3, we read from `placeholderColor` which is why we should
use `--placeholder-color` here as well.


https://github.com/tailwindlabs/tailwindcss/blob/f38be227df384504a170409c2131ca5ca8bfe025/src/corePlugins.js#L2317

That said, this is technically a breaking change in case somebody relies
on `--background-color` for `placeholder` values. But since this is text
related, and most people will rely on the default `--color` values
instead, I think it's safe to change this as-is.

In the unlikely event that somebody _does_ rely on this, then we have 2
options:

1. Guide them to make use of `--placeholder-color` instead (preferred
solution)
2. Re-add `--background-color` after the `--placeholder-color` (band-aid
solution, but might be worth it who knows)

Fixes: #19838

## Test plan

1. Existing tests still pass
2. Verified in the Tailwind CSS v3 codebase that we did read from
`placeholderColor` which in turn reads from `color` by default. Which is
equivalent to `--placeholder-color` and `--color` in Tailwind CSS v4.

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Canonicalization: collapse `scroll-p{t,b}-*` into `scroll-py-*`, `scroll-p{l,r}-*` into `scroll-px-*`, and `scroll-p{t,r,b,l}-*` into `scroll-p-*` ([#19842](https://github.com/tailwindlabs/tailwindcss/pull/19842))
 - Canonicalization: collapse `overflow-{x,y}-*` into `overflow-*` ([#19842](https://github.com/tailwindlabs/tailwindcss/pull/19842))
 - Canonicalization: collapse `overscroll-{x,y}-*` into `overscroll-*` ([#19842](https://github.com/tailwindlabs/tailwindcss/pull/19842))
+- Read from `--placeholder-color` instead of `--background-color` for `placeholder-*` utilities ([#19843](https://github.com/tailwindlabs/tailwindcss/pull/19843))
 
 ## [4.2.2] - 2026-03-18
 

packages/tailwindcss/src/utilities.ts

@@ -3960,7 +3960,7 @@ export function createUtilities(theme: Theme) {
   ])
 
   colorUtility('placeholder', {
-    themeKeys: ['--background-color', '--color'],
+    themeKeys: ['--placeholder-color', '--color'],
     handle: (value) => [
       styleRule('&::placeholder', [decl('--tw-sort', 'placeholder-color'), decl('color', value)]),
     ],