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\documentclass{article}
\usepackage[a4paper,top=3cm,bottom=1.5cm,left=3.5cm,right=0.75cm]{geometry}
\usepackage{helvet}
\renewcommand{\familydefault}{\sfdefault}
\title{Title}
\author{John Smith}
\usepackage[hidelinks]{hyperref}
\usepackage[dvipsnames]{xcolor}
\usepackage{tikz}
\usepackage{lipsum}
\usepackage{picture,calc}
\usepackage{fancyhdr}
\def\colstripe{
\AtBeginShipoutNext{\AtBeginShipoutUpperLeft{%
\put(0,-\paperheight){{\color{Red}\rule{3cm}{\paperheight}}} %
}
}
}
\fancypagestyle{plain}{ %
\fancyhead{\colstripe}
\renewcommand{\headrulewidth}{0pt}
\renewcommand{\footrulewidth}{0pt}
}
\pagestyle{plain}
\begin{document}
\maketitle
\lipsum[1-100]
\end{document}
Sample Output:

backgroundpackage. Possible dupe: How to set colored ruled margins for different pages? – Jan 24 '13 at 14:10