[NTG-context] Error using \starttextbackground.

8 Apr 2003

      I want a gray background in a particular column.
Here is some pertinent code (copied from details.pdf)

\definetextbackground[bar]
[backgroundcolor=textgray,
backgroundoffset=.25cm,
offset=.5cm,
frame=off,
location=paragraph,
color=black]
...and here is where I want the background:
\column
\starttextbackground[bar]
This is column three text with background and all kinds of
other stuff.
\stoptextbackground
...and here is the compile error:
-----------------------------------------------
   generating graphics : metaposting mpgraph.mp

 TeXExec 3.2 - ConTeXt / PRAGMA ADE 1997-2003

              metapost : mpgraph
                format : metafun
This is MetaPost, Version 0.641 (Web2C 7.3.7x)
(mpgraph.mp
...
...
spotcolors
true
! Equation cannot be performed (numeric=boolean).
<to be read again>
                   ;
l.23 spotcolors := true ;

If I use \startbackground(etc) in the same spot
I get no error but I don't like the quality.

Hints?

John Culleton