Possible to Match the Colors of Crowns and Veneers?

Without question crowns and veneers can be matched to look the same.  The question is what kind of crowns do you have?  Are your current crowns all porcelain or to they have any metal in them.  If they are porcelain fused to metal crowns they will be much more difficult to match because they reflect light differently than do all porcelain crowns.  In that case I would replace the two crowns when you are doing the others.  If they are all porcelain, a very high end dental lab can match them off of digital pictures taken by your cosmetic dentist. 

Quite often the color of a front tooth is very different than the side tooth, and communicating shades to labs can be a big challenge (photographs can shift colors, monitors are different, etc).
The most predictable method is to have all teeth restored at the same time by the same lab technician with the same material (including the ones already done).  This way all colors are mapped correctly and everything can match as well as possible.  The fee may be a little more, but the results are worth it.
Anything less is a compromise and expectations should be lower.

It will be a little hard.

There will always be a very slight difference because of the thickness of the materials.

All crowns is a solution but might be a little aggressive.

Make sure you have the technician who will make your crowns/veneers see photos of the teeth after they are prepared/exposed.

Your dentist will help you with that.

Dr.K.

The most important factor in successful matching is the skill of the cosmetic team you are working with. A skillful ceramist can match anything, but that said, it may be difficult to do and they may need a few tries to do it so you can expect to pay more if you are demanding a single tooth be matched to another if it is a difficult match.
If you are changing out the crowns and doing all the veneers at the same time it can become a lot easier to match and the dentist and ceramist can create a more predictable outcome. I would recommend replacing everything all at once to make it more predictable.

If you have a good lab and an experienced dentist you should not have any problems. Before he or she cements them have them try them in your mouth and see if you like them..if they dont match then have them remade...Your DDS should be willing to do that for you.