Unfortunaly there is no MWE in the question and the OP does not say, if one or all page styles should be modified or if a new page style should be defined to get the empty header with an orange separation line.
To modify all layer page styles:
\AddToLayerPageStyleOptions{@everystyle@}
{oninit=%
\KOMAoptions{headsepline,plainheadsepline}\setkomafont{headsepline}{\color{orange}}%
\ihead*{}\chead*{}\ohead*{}%
}
To modify one layer page style including the related plain
style, eg. thesisSimple
:
\AddToLayerPageStyleOptions{thesisSimple}
{oninit=%
\KOMAoptions{headsepline}\setkomafont{headsepline}{\color{orange}}%
\ihead{}\chead{}\ohead{}%
}
\AddToLayerPageStyleOptions{plain.thesisSimple}
{oninit=%
\KOMAoptions{headsepline,plainheadsepline}\setkomafont{headsepline}{\color{orange}}%
\ihead*{}\chead*{}\ohead*{}%
}
Defining a new pair of layer page styles:
\providepairofpagestyles{myThesis}{%
\clearpairofpagestyles
\ifoot[\currentpagestyle: inner footer]{inner footer}
\cfoot*{\pagemark}
\ofoot[outer footer]{\currentpagestyle: outer footer}
}
\AddToLayerPageStyleOptions{myThesis}
{oninit=\KOMAoptions{headsepline}\setkomafont{headsepline}{\color{orange}}}
\AddToLayerPageStyleOptions{plain.myThesis}
{oninit=\KOMAoptions{headsepline,plainheadsepline}\setkomafont{headsepline}{\color{orange}}%
}
Example:
\documentclass{book}
\usepackage{xcolor}
\usepackage[markcase=used]{scrlayer-scrpage}
\providepairofpagestyles{thesisSimple}{%
\clearpairofpagestyles%
\automark[chapter]{chapter}
\ihead{\headmark}% Inner header
\ohead[\pagemark]{\pagemark}% Outer header
}
\ifoot{}% Inner footer
\ofoot{}% Outer footer
\pagestyle{thesisSimple}
\providepairofpagestyles[thesisSimple]{thesis}{%
\automark*[section]{}%
}
\providepairofpagestyles[thesisSimple]{review}{%
\ofoot[\shorttitle/\authorname]{\shorttitle/\authorname}
\ifoot[\today]{\today}
}
\pagestyle{thesis}
\newcommand*\shorttitle{Short Title}
\newcommand*\authorname{Author Name}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%% modify all layer page styles:
\AddToLayerPageStyleOptions{@everystyle@}
{oninit=%
\KOMAoptions{headsepline,plainheadsepline}\setkomafont{headsepline}{\color{orange}}%
\ihead*{}\chead*{}\ohead*{}%
}
%%%%
% or
%%%% modify one layer page style and its plain style
%\AddToLayerPageStyleOptions{thesisSimple}
%{oninit=%
%\KOMAoptions{headsepline}\setkomafont{headsepline}{\color{orange}}%
%\ihead{}\chead{}\ohead{}%
%}
%\AddToLayerPageStyleOptions{plain.thesisSimple}
%{oninit=%
%\KOMAoptions{headsepline,plainheadsepline}\setkomafont{headsepline}{\color{orange}}%
%\ihead*{}\chead*{}\ohead*{}%
%}
%%%%
% or
%%%% new pair of layer page styles:
%\providepairofpagestyles{myThesis}{%
%\clearpairofpagestyles
%\ifoot[\currentpagestyle: inner footer]{inner footer}
%\cfoot*{\pagemark}
%\ofoot[outer footer]{\currentpagestyle: outer footer}
%}
%\AddToLayerPageStyleOptions{myThesis}
%{oninit=\KOMAoptions{headsepline}\setkomafont{headsepline}{\color{orange}}}
%\AddToLayerPageStyleOptions{plain.myThesis}
%{oninit=\KOMAoptions{headsepline,plainheadsepline}\setkomafont{headsepline}{\color{orange}}%
%}
%%%%
\usepackage{blindtext}% only for dummy text
\begin{document}
\blinddocument
\cleardoublepage
\pagestyle{thesisSimple}
\blinddocument
\IfLayerPageStyleExists{myThesis}{
\cleardoublepage
\pagestyle{myThesis}
\blinddocument
}{}
\cleardoublepage
\pagestyle{review}
\blinddocument
\end{document}