Colored mark in margin notes in the middle of the \marginparsep

Question

It's code, thanks for @Harish Kumar,

\documentclass{book}
\usepackage{mathtools}
\usepackage{xcolor}
\definecolor{background}{RGB}{255,255,170}
\usepackage{empheq}
\newcommand*\mybox[1]{%
\colorbox{background}{\hspace{1em}#1\hspace{1em}}}
\usepackage{kantlipsum}
\usepackage[fulladjust]{marginnote}
\setlength{\marginparsep}{5mm}
\setlength{\marginparwidth}{1in}
\begin{document}
\begin{empheq}[box=\mybox]{align}R_A+R_B &=\frac{R_3(R_1+R_2){R_1+R_2+R_3}\marginnote{Some margin note here}
\end{empheq}
\clearpage
\begin{empheq}[box=\mybox]{align}R_A+R_B &=\frac{R_3(R_1+R_2)}{R_1+R_2+R_3}\marginnote{Some margin note here}
\end{empheq}
\end{document}

It's code very well working. That I want add to colored mark in margin notes in the middle of the \marginparsep. Odd page \blacktriangleleft and even page \blacktriangleright. Like that,

\checkoddpage
\ifoddpage
\newcommand{\marginmacro}{\marginnote{ {\color{red}$\blacktriangleleft$} Some margin note here}}
\else
\newcommand{\marginmacro}{\marginnote{Some margin note here {\color{red}$\blacktriangleright$}}}
\fi

That is, add first attach red color \blacktriangleleft in the middle of \marginparsep add second attach margin not in the \marginnote area in the odd pages. In the other hand, add first attach margin not in the \marginnote area, add second attach red color \blacktriangleleft in the middle of \marginparsepin the even pages.

For example, for odd pages.

I'm sure this is a duplicate of another question that I just can't find. So, does anyone know how to fix it?

Answer 1

There you go again:

\documentclass{book}
\usepackage{mathtools,amssymb,ifoddpage,showframe}   %% remove showframe.

\usepackage{xcolor}
\definecolor{background}{RGB}{255,255,170}
\usepackage{empheq}
\newcommand*\mybox[1]{%
\colorbox{background}{\hspace{1em}#1\hspace{1em}}}
\usepackage{kantlipsum}
\usepackage[fulladjust]{marginnote}
\setlength{\marginparsep}{5mm}
\setlength{\marginparwidth}{1in}
\newcommand{\mymarginnote}[1]{%
\checkoddpage
\ifoddpage
\marginnote{\hspace*{-0.55\marginparsep}\makebox[0pt]{\textcolor{red}{$\blacktriangleleft$}}\hspace{0.55\marginparsep}#1}
\else
\marginnote{\makebox[0pt][l]{\makebox[\dimexpr\marginparwidth+0.77\marginparsep\relax][r]%
 {\textcolor{red}{$\blacktriangleright$}}}\hfill#1}
\fi
}
\begin{document}
  \kant[1]
  \begin{empheq}[box=\mybox]{align}
     R_A+R_B &=\frac{R_3(R_1+R_2)}{R_1+R_2+R_3}\mymarginnote{Some margin note here}
  \end{empheq}
  \kant[2]
  \clearpage
  \kant[1]
  \begin{empheq}[box=\mybox]{align}
     R_A+R_B &=\frac{R_3(R_1+R_2)}{R_1+R_2+R_3}\mymarginnote{Some margin note here again}
  \end{empheq}
  \kant[2]

\end{document}