It is possible to customise DuckDuckGo for yourself using the settings page. Customisations include changing the site’s colours and fonts, but also behaviour, like infinite scrolling and whether the header appears.

Of particular interest to me is that these settings can be modified using query strings. Thus, when you use the search form, the search results page at DuckDuckGo uses colours from my site.

The colour values and other customisations are fed to DuckDuckGo via hidden fields in the search form. For example:

<input type="hidden" name="kj"  value="#41072A"><!-- header-->
<input type="hidden" name="k8"  value="#333333"><!-- text -->
<input type="hidden" name="k9"  value="#C00076"><!-- links -->
<input type="hidden" name="kx"  value="#B4B4B4"><!-- url -->

The work of getting the search from here to DuckDuckGo is handled by redirect rules in my web server configuration. In part because of how I’ve set that up, searching using the https://nostodnayr.net/search/query syntax isn’t customised. It should be possible to make it work, but not really worth the effort.