Now I have to change the color of numbers just before the footnote text so that it can match the color of text area.  I try to do it like this:
 
\def\myfootnotecolor#1{%
    \startcolor[red]#1\stopcolor}
 
\setupfootnotes
   [numbercommand={\myfootnotecolor}]
 
or
 
\setupfootnotes
   [foregroundcolor=red]
 
either method has no effect.