\starttext

It seems that the problem comes up when the same color as the surrounding text is used in MPcode.\par
{
  \red
  text red\par
  \startMPcode
    drawoptions(withcolor blue);
    label("text blue in MPcode", origin);
  \stopMPcode
  \par
  text still red\par
  But\par
  text red\par
  \startMPcode
    drawoptions(withcolor red);
    label("text red in MPcode", origin);
  \stopMPcode
  \par
  text turns black\par
  Can get over with this:\par
  text red\par
  \startMPcode
    drawoptions(withcolor red);
    label("text red in MPcode", origin);
    label("\null", origin); % add this seems to solve the problem
  \stopMPcode
  \par
  text still red\par
  Don't know why. Just an observation.
}

\stoptext