add changelog item

[skip ci]

Author: cderv

news/changelog-1.7.md

@@ -51,6 +51,10 @@ All changes included in 1.7:
 - ([#11835](https://github.com/quarto-dev/quarto-cli/issues/11835)): Take markdown structure into account when detecting minimum heading level.
 - ([#11964](https://github.com/quarto-dev/quarto-cli/issues/11964)): Using panel layout without a crossref label now correctly do not add an empty `#block[]` that was leading to an unnecessary space in output.
 
+## `revealjs` format
+
+- ([#12147](https://github.com/quarto-dev/quarto-cli/issues/12147)): `serif` and `simple` themes defaults back to have their heading color (`$presentation-heading-color`) to be the same as the body color (`$body-color`) as in Quarto 1.5.
+
 ## Interactive Shiny Document
 
 - ([#12059](https://github.com/quarto-dev/quarto-cli/issues/12059)): `quarto preview` now correctly run on Windows an interactive Quarto doc with Jupyter engine and py-shiny, when using a `*.py` file as resource.