You can certainly use conditional format to change the text color to grey, but conditional formatting will not affect the field's behavior. Search this forum for threads on "locking a record" (the advanced link works best) and you should be able to find a good description of how to use accounts and privileges to do the locking part.
Let's say you want the fields to be grey when a checkbox formatted field has "locked" in it and normal format if it is empty:
Use the formula option to enter:
Not Isempty (table::lockfield)
as the expression on each field you want to show grey (You can select all the fields and apply this conditional format once for all of them.).
Now select a grey text color for it and the appearnce part is done.