documentclass{article}
usepackage[dvipsnames]{xcolor}
usepackage{colortbl}
usepackage{siunitx}
newcommand{green}{fboxsep=0.2mm fboxrule=1mmfcolorbox{white}{green}{color{green}{a}}}

begin{document}

begin{table}
centering
setlength{tabcolsep}{0.9pt}
sisetup{round-mode = places,round-precision = 0,table-format = 4.1}
begin{tabular}{lS}
BLAH&{textsuperscript{}}1235.6419316{textsuperscript{+}}cellcolor{green}\
end{tabular}
caption{green denotes ...}
end{table}

end{document}

setlength{tabcolsep}{0.9pt}