How to write this kind of colour text in LaTeX?

I've noticed that the OP has already accepted one of the answers provided so far. Just to provide some variety, here's a solution that provides a LaTeX macro called \boldredcaps which renders all uppercase letters in its argument in bold and red automatically. No need to apply lots of \textbf{\textcolor{red}{...}} instructions by hand. The LaTeX macro \boldredcaps relies on Lua's powerful gsub string function to accomplish its job.

% !TEX TS-program = lualatex
\documentclass[12pt]{article}
\usepackage{xcolor}   % for "\textcolor" macro
\usepackage{ragged2e} % for "\Centering" macro
\usepackage{luacode}  % for "\luaexec" macro
%% Define a LaTeX macro called "\boldredcaps":
\newcommand\boldredcaps[1]{\luaexec{%
   yyy = "#1"
   yyy = yyy:gsub ( "\%u" , "\\textbf{\\textcolor{red}{\%0}}" )
   tex.sprint ( yyy )
}}

%% Concoct steganographic message:
\newcommand{\blurb}{Since Everyone Can Read, Encoding Text In Neutral Sentences Is Doubtfully Effective.}

\begin{document}

\begin{figure}
\Large  % or "\large", or "\huge", etc
\sffamily\itshape
\Centering
\boldredcaps{\blurb} % <-- argument of \boldredcaps can be a macro 

\bigskip
\textbf{\textcolor{red}{`secret inside'}}
\rmfamily\upshape
\caption{Text Steganography}
\end{figure}

\end{document}

If you need to do this often, it can be automated with the xstring using \StrSubstitute to replace a space with \textcolor{red}:

Code:

\documentclass{article}
\usepackage{xcolor}
\usepackage{xstring}

\newcommand*{\Hightlight}[1]{%
    \noexpandarg
    \StrSubstitute[0]{\textcolor{red}#1}{ }{ \textcolor{red}}[\FormattedString]%
    \FormattedString%
}%

\begin{document}
\Hightlight{Since Everyone Can Read, Encoding Text In Neutral Sentences Is Doubtfully Effective} 
\end{document}

Like this?

\documentclass{article}

\usepackage{xcolor}

\begin{document}

\begin{center}
    \Large\sl
    \textcolor{red}{S}ince \textcolor{red}{E}veryone \textcolor{red}{C}an \textcolor{red}{R}ead, \textcolor{red}{E}ncoding \textcolor{red}{T}ext \textcolor{red}{I}n \textcolor{red}{N}eutral \textcolor{red}{S}entences \textcolor{red}{I}s \textcolor{red}{D}oubtfully \textcolor{red}{E}ffective

    \vspace{1cm}\LARGE\color{red}
    `Secret inside'
\end{center}

\end{document}