Dennis,

I did the same thing yesterday :) thought I was going crazy. Is it possible that the field is a character and not a numeric?

this is what happened to me, no data type mismatch errors etc., just a white line.

also, you don't need the quotes around the expression:

"IIF(lvSchedule.order_display=0,RGB(255,255,255),IIF(lvSchedule.order_display>0,RGB(128,255,128),RGB(255,255,128)))"

i.e.

IIF(lvSchedule.order_display=0,RGB(255,255,255),IIF(lvSchedule.order_display>0,RGB(128,255,128),RGB(255,255,128)))

hope this helps