dba56 wrote:
Is it possible to apply brick veneer to a brick chimney on the side of
a house? We would like to cover the red brick with grey brick veneer
to match our grey siding?

Possible? Yes.
Economical? Maybe not.
Talk to a masonry contractor to assess what is involved. You may need a
veneer footing or support, and a lot of anchors installed for the new
brick. Will the added proportions of the modified chimney look right
with the house?
Consider painting the current brick as well, get an estimate. Compare
both and decide what you like best. Good luck.

Joe