Introductory pages don't inherit plain pagestyle definitions

Question

I'm compiling a report with custom headers and footers, using the scrreprt document class. I have redefined the headers and footers of the plain pagestyle through the scrpage2 package, but the redefined style doesn't apply for the table of contents or anything before that (ref. the code below).

How do I make my redefined plain pagestyle apply to the entire document?

\documentclass[11pt,b5paper,twoside,openright,parskip=full,abstract=true,BCOR=0.5cm]{scrreprt}
\usepackage[automark,headsepline,plainheadsepline]{scrpage2}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern,microtype}
\usepackage{parskip,titlesec}
\usepackage{xcolor}
\usepackage{lipsum}

\addtokomafont{disposition}{\rmfamily}
\KOMAoptions{numbers=noendperiod}

\ihead[]{\headmark}
\ohead[\pagemark]{\pagemark}
\ofoot[]{}
\setheadsepline{0.5pt}[\color{black!60!white}]
\renewcommand*{\chaptermarkformat}{\chapapp~\thechapter\autodot:\enskip}



\begin{document}

\pagenumbering{roman}

\begin{abstract}
\thispagestyle{plain}
\noindent \lipsum[1-2]
\end{abstract}

\chapter*{Acknowledgments}
\lipsum[1-2]

\chapter*{Possibly another introductory chapter}
\lipsum[1-2]

\tableofcontents


\chapter{First chapter}
\pagenumbering{arabic}
\pagestyle{scrheadings}
\lipsum [1-3]


\section{Text train}
\lipsum[1-15]

\end{document}

Answer 1

Add the following to your preamble after loading scrpage2:

\pagestyle{scrheadings}