<context source=yes>
\setuppapersize[A5]
\setupcolors[textcolor=redblue] % text color\setupcolumns[rule=on] % there’s no key for "rule color"!
\color[bluered] % rule color, but might set influence also the color of other elements, too!\startcolumns[n=23,rule=on]\input tufte \column
\input knuth
\stopcolumns