well now..
first of all i think we found a bug in CS5 at least. Please (anyone) try to duplicate my problem:
1) open the Find Object dialog
2) In the Find Object Format select the Fill Color Black. (Click a few times on Find/Find Next just to be sure)
3) open ESTK, link it to indesign, open the console and type:
app.findObjectPreferences.fillColor.name
i get: Result: Yellow
4) in the ESTK Console, type
app.findObjectPreferences.fillColor='Black'
in the Find Object Format dialog, you will get: Fill: Color: (Unnamed Color) Click the Find Button, and "Nothing found"
5) now for the fun part, in the ESTK Console type:
app.findObjectPreferences.fillColor='Yellow'
in the Find Object Format dialog, you will get: Fill: Color: [Black]. Clicking on the Find Button you will get the (un)expected results.
a bit later, apparently is not a new bug: http://forums.adobe.com/message/2914093