LandmarkValue

Here's a way to do something similar. Plot this data using an Area chart:

Fake Real
Bob 2 1
Chuck 2 4
Dog 2 3

In this example, the fake series, 2 is where we want the threshold (your colored gridline)
The real series will be on top of the fake one. Right click it, and change the chart type
to line. Now the line will be drawn over the gridline, which will indicate the threshold.
You can set the color of the fake area to none, and change the line to the color you want.
It will look similar to your request.

--
Earl Kiosterud
www.smokeylake.com

Note: Top-posting has been the norm here.
Some folks prefer bottom-posting.
But if you bottom-post to a reply that's
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When in Rome...
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"LandmarkValue" wrote in message
...
I am trying to change the color of one of the gridlines in my line chart (not
all of them). Since I have not seen any sort of formatting option along these
lines, I used the autoshapes function to simply add a colored line on top of
the desired gridline; however, I want to be able to update/add data for the
graph, and still have the colored line stay where its supposed to when the
graph changes. Is this possible?