minor edit

Author: gordonwoodhull

docs/extensions/brand.qmd

@@ -91,6 +91,8 @@ The example brand.yml is using the unified light and dark brand feature. Documen
 
 Any color in the color or typography sections of [brand.yml](https://posit-dev.github.io/brand-yml/) can be specified with `light` and `dark` components or as a string. If a string, the value is used for both light and dark modes.
 
+This works for colors only.
+
 :::
 
 ## How Brand Extensions Work