Hi, Eric,
A quick response - try to drill down into the report after you instantiate it....you may need to use the debugger to check out the objects, but something like...
oMyReport.ReportDefinition.Areas[1].Sections[1].ReportObjects
...should give you access to the chart object, and possibly the means to change a slice color.
I'm jammed up right now, but give that a try - if that doesn't work, let me know and I'll take another look later.
Kevin