Java JCEF set header prefered colour scheme

I would need to set a preferred color scheme in the URL request header.

I tried this code:

HashMap<String, String> headerMap = new HashMap<String, String>();                    
cr.getHeaderMap(headerMap);
cr.getHeaderMap(headerMap);

headerMap.remove("Sec-CH-Prefers-Color-Scheme");
headerMap.put("Sec-CH-Prefers-Color-Scheme", app.colorScheme);                    
cr.setHeaderMap(headerMap);

This code is called from:

addRequestHandler :: onBeforeBrowse

When I looked for solution, I found example where was headers changed call from onBeforeBrowse, but this method no longer exists or I coud not found it.

Sending of headers I tested on:
https://www.whatismybrowser.com/detect/what-http-headers-is-my-browser-sending

Anybody know solution? Thanks.