Conditional Formatting Colour and Text Entries

Please read the whole blurb. Maybe there is a better way!!

Question 1:
How to conditional format cells with Text drop-down list
Question 2:
How to insert " ?? " in cell when no valid/acceptable text or number is
in cell.
To clarify:
Have large number of cells that are "unprotected".
As I make changes to WB, I periodically activate macro that makes all
unprotected cells yellow and protected cells white.
When WB gets printed, part of the special printing instructions includes
code that removes all colour from WB.
NOW:
1: I need to hi-lite critical cells, so they print with a Different Colour
(light blue),
if no entry is made in that cell.
Have determined that Colours created with conditional formatting do NOT
get removed by my special print code. - GOOD!!
Conditional format those cells with "not equal to" "0", then format
light blue.
If appropriate number is entered, cell reverts back to yellow.

Q1: Cells that have (text) drop down list. (yes, no, maybe)
How to conditional format them, so that if a drop down option is
selected,
the cells reverts back to yellow.

Q2: How to insert " ?? " in cell when no valid/acceptable text or number is
in cell.
that is, all the light blue cells should have the double question
marks in them,
until a valid entry is made in that cell, and the cell becomes yellow
again.

This is just the first step of many.
The NEW 1st step of my special printing code will be:
1: Check for Blue cells with ??. If found, a corresponding warning message
gets flashed on the screen. 8 Blues, then 8 messages
2: If there are ANY blue cells with ??, then ONE email will be sent to the
issuing salesman (and others), as a reminder/notification/ of outstanding
issues.