SP 2010 - Lookup Column not working with Conditional Formatting

I have a lookup column for Tabs:

Major

Sub-1

Sub-2

Sub-3

Technical

Pricing

I need to setup conditional formatting so the row color changes with the level of tab selected. I can do this with drop down columns, but it is not working with lookup?

Is there a work around for this? If not how do I have a drop down that will not give me an error if there is no blank option?