rdlc background color expression

dear peepz,

just want to check whether i am doing this right, i am using visual studio 2008 and have inserted an expression in the backgroundcolor properties for one of the textbox in the table which is suppose to highlight the textbox accordingly. the expression is:-

=iif(fields!element1.value = "hello", "Red", "White")

but however, the expression did not seem to take any effect on the textbox and remain transparent.

advise please...thanks in advance...

regards,
farah k.