How to have colored headings with one color per chapter

Question

I'm typesetting a proceedings-style book that contains articles in their chronological order. Since the articles are also categorized, each category is assigned a color and the the chapter styles are supposed to use that color as background color for some fancy chapter art. This part works as expected with titlesec.

In addition to that, I'd like to also change the color of the headings, which should be the same "chapter color" for the current chapter.

The problem I observe with my naive approach is that the headings color is changed too early, i.e. the page before the new chapter is already printed with the new color.

Here is a MWE:

\documentclass[fontsize=12pt, paper=a4]{scrbook} 
\usepackage[ngerman]{babel}
\usepackage{blindtext}
\usepackage[automark]{scrpage2} 
\usepackage{xcolor}

\newcommand{\chaptercolor}{red}

\clearscrheadfoot 
\pagestyle{scrheadings}
\ihead[\color{\chaptercolor}\leftmark]{\color{\chaptercolor}\leftmark} 
\ohead[\color{\chaptercolor}\rightmark]{\color{\chaptercolor}\rightmark}
\cfoot[\color{\chaptercolor}\pagemark]{\color{\chaptercolor}\pagemark}

\begin{document} 

\renewcommand{\chaptercolor}{blue}
\chapter{Ch1}
\Blindtext

\renewcommand{\chaptercolor}{green}
\chapter{Ch2}
\Blindtext

\end{document}

As you can see, on page 2 the heading is already green although this page still belongs to chapter 1, which is supposed to be blue.

What I also tried was to use two different variables (headercolor and chaptercolor), where I used \headercolor in the *head statements and used titlesec's \titelformat to assign the chaptercolor to the headercolor only when the chapter title itself is set. Unfortunately this didn't work either.

Update: I'm looking for a preamble solution. The MWE oversimplifies my current script and since the color is also used in the chapter title itself, it is important that the chapter color is defined before the chapter starts. I'd like to keep this kind of "interface" as stable as possible so that authors don't need to mess with details.

Any advise on how I can lazily set the color so that the color change in the headings happens only on the very first page of the new chapter is highly appreciated. Thanks!

Answer 1

As mentioned in the comments, it is sufficient to place the colorchange (done via \chaptercolor) after calling the chapter command.

\documentclass{scrbook} 
\usepackage{blindtext}
\usepackage[automark]{scrlayer-scrpage}
\usepackage{xcolor}

\clearscrheadfoot 
\ihead[\leftmark]{\leftmark} 
\ohead[\rightmark]{\rightmark}
\cfoot[\pagemark]{\pagemark}
%Now adding color to all elements in the pagehead
%This is much easier to maintain
\addtokomafont{pagehead}{\color{\chaptercolor}}

\begin{document} 

\chapter{Mark Twain}
\newcommand{\chaptercolor}{blue}
\Blindtext

\chapter{Ambrose Bierce}
\renewcommand{\chaptercolor}{green}
\Blindtext

\end{document}

But i would prefer seeing normal black text on a mild colored background. For a one sided document you can define something like this

\DeclareLayer[clone=plain.scrheadings.head.oneside,
    contents={%
        \color{\chaptercolor}%
        \rule[-\dp\strutbox]%
        {\paperwidth}{\headheight}%
    }%
]{plain.scrheadings.head.oneside.background}
\DeclareLayer[clone=scrheadings.head.oneside,
    contents={%
        \color{\chaptercolor}%
        \rule[-\dp\strutbox]%
        {\paperwidth}{\headheight}%
    }%
]{scrheadings.head.oneside.background}

Resulting in the follwing output:

Another thing that might be worth a look gives this output

This can be achieved using the following code.

\documentclass{scrbook} 
\usepackage[ngerman]{babel}
\usepackage{blindtext}
\usepackage[automark]{scrlayer-scrpage}
\usepackage{xcolor}


\clearscrheadfoot 
\ihead[\leftmark]{\leftmark} 
\ohead[\rightmark]{\rightmark}
\cfoot[\pagemark]{\pagemark}


%Defining the Layer
\makeatletter
\newlength{\topheight}
\setlength{\topheight}{\sls@topmargin}
\addtolength{\topheight}{\headheight}
\DeclareLayer[
    background,
    contents={%
        \color{\chaptercolor}%
        \rule{\paperwidth}{\topheight}%
    }%
]{scrheadings.head.background}
\makeatother

%Adding the Layer to the pagestyles
\AddLayersAtBeginOfPageStyle{scrheadings}{%
    scrheadings.head.background,%
}
\AddLayersAtBeginOfPageStyle{plain.scrheadings}{%
scrheadings.head.background}

\usepackage{etoolbox}
\newcommand{\basecolor}{%
    \ifcase\arabic{chapter}\or blue\or orange\or green\or red\fi%
}
\newcommand{\chaptercolor}{\basecolor!20!white}
\begin{document} 

\chapter{Mark Twain}
\Blindtext
\Blindtext
\chapter{Walt Whitman}
\Blindtext
\Blindtext
\Blindtext
\chapter{F. Scott Fitzgerald}
\Blindtext
\Blindtext
\chapter{Ambrose Bierce}
\Blindtext
\Blindtext
\end{document}

You can make it even more fancy by changing the color of the chapter title by adding

\newcommand{\chaptertitlecolor}{\basecolor!70!white}
\addtokomafont{chapter}{\color{\chaptertitlecolor}}

Both, the colored bar on top and the title share the same basecolor. But i decided to go for a darker variant for better readability. The output looks like this:

One could even go further and print the header in a darker shade of the basecolor, which could look something like this

Please Remember

Colours can be very distracting and disturb the readability. Printing coloured pages is also quite expensive.

Answer 2

Define a new command wich executes \cleardoublepage and changes the color:

\newcommand{\changechaptercolor}[1]{%
  \cleardoublepage%
  \renewcommand\chaptercolor{#1}%
}

Then you can use

\documentclass[fontsize=12pt]{scrbook} 
\usepackage[ngerman]{babel}
\usepackage{blindtext}

\usepackage{xcolor}
\newcommand\chaptercolor{red}
\newcommand{\changechaptercolor}[1]{%
  \cleardoublepage%
  \renewcommand\chaptercolor{#1}%
}

\usepackage[automark]{scrpage2}% or scrlayer-scrpage
\clearscrheadfoot 
\pagestyle{scrheadings}
\addtokomafont{pageheadfoot}{\color{\chaptercolor}}
\addtokomafont{pagenumber}{\color{\chaptercolor}}
\ihead[\leftmark]{\leftmark} 
\ohead[\rightmark]{\rightmark}
\cfoot[\pagemark]{\pagemark}

\begin{document} 
\changechaptercolor{blue}
\chapter{Ch1}
\Blindtext

\changechaptercolor{green}
\chapter{Ch2}
\Blindtext
\end{document}