newcommand{rtext}[1]{%
{color{blue}smalltexttt{detokenize{#1}}}%
}

documentclass{article}
newcommand{rtext}[1]{%
{color{blue}smalltexttt{detokenize{#1}}}%
}
begin{document}
rtext{%>%}
end{document}

Runaway argument?
{end {document}
! File ended while scanning use of rtext.
<inserted text>
                par