rdlc background color bug - large expression seems to cause a bug - asp.net

Question

I am working on designing a rather large rdlc report in ASP.Net MS visual 2010. Some rows in the report require the row to be highlighted if something is out of place. So I went to the background colors tab in the Properties box of my rdlc report after clicking on the table row. I am trying to get the following expression to work in the background color tab in the properties box.
`=IiF((Fields!C.Value < .75 And Fields!C.Value <> "")
Or (Fields!S.Value < .75 And Fields!S.Value <> "")
Or (Fields!O.Value > 5), "Yellow", "White")`
Originally I want the background color either yellow or white, but for testing purposes I changed white to green since white is a default it seems.
`=IiF((Fields!C.Value < .75 And Fields!C.Value <> "")
Or (Fields!S.Value < .75 And Fields!S.Value <> "")
Or (Fields!O.Value > 5), "Yellow", "Green")`
This caused some rows to be green, but none were yellow, the rows that should be yellow are instead white.
It works fine when I shorten it to
`=IiF((Fields!C.Value < .75 ), "Yellow", "Green")`
I get all Green and Yellow rows.
And it worked fine when I tried
`=IiF((Fields!C.Value < .75 And Fields!C.Value <> ""), "Yellow", "Green")
This worked fine too I get all rows being either Green or Yellow.
But as soon as I add an Or they stop working.
`=IiF((Fields!C.Value < .75 And Fields!C.Value <> "")
Or Fields!O.Value > 5 , "Yellow", "Green")`
This results in some Green rows but no yellow rows, the should be yellow rows all come out white?
And in some cases I get no Green or Yellow rows. I tired in versing the original statement,
`IiF((Fields!Cpk_C.Value >= .75 Or Fields!Cpk_C.Value = "")
And (Fields!Cpk_S.Value >= .75 Or Fields!Cpk_S.Value = "")
And (Fields!Cpk_S.Value <= 5), "Green", "Yellow")`
but then nothing works as it's all white rows.
Any help in what I am doing wrong, or why this doesn't work, is appreciated, thanks.

Answer 1

As shown in the comments above the problem was solved (thanks to a tip from Ic). The issue had to do with the type of values the items C.Value and S.Value. They were Decimal based and not string so a comparison to <> "" was causing a format warning which wouldn't execute the code on those rows resulting a no color applied as a result. Since they were essentially floats the IsNumeric function was a better fit.
=IiF((Fields!Cpk_C.Value > .75 And IsNumeric(Fields!Cpk_C.Value)) Or (Fields!Cpk_S.Value > .75 And IsNumeric(Fields!Cpk_S.Value)) Or Fields!OOC.Value > 5, "Yellow", "White")