You would need to pass the amount from the main report to the subreport in a shared variable. In the main report, create a formula:
whileprintingrecords;
shared currencyvar hrrate := {table.hrrate};
Place this in a section of the main report above the one containing the sub, e.g., if the sub is in GHb, place the formula in GHa. Then in the subreport, you can select the corresponding field->format field->borders->color->background->x+2 and enter:
whileprintingrecords;
shared currencyvar hrrate;
if currentfieldvalue <> hrrate then
cryellow else
crnocolor
You should add a reset formula in the main report, in a section after the subreport, e.g., GHc, which can be suppressed:
whileprintingrecords;
shared currencyvar hrrate := 0;
-LB