Veneer Color Change Before Procedure?

We we cement veneers we can make minor changes using different colored cements. If its a huge deal breaker then the veneers need to be remade which is costly.

It's beneficial to everyone involved that BEFORE the veneers are bonded to the tooth structure permanently that you go through a try-in phase (sometimes even with try-in gel to replicate what the underlying cement will do). 

Veneers look very different just examining them on a model vs. visualizing them in the mouth with a try-in gel.  This because the veneer gets a lot of it's color characteristic from the color of the underlying tooth structure in some cases.