What is the best way to dye a white cotton button-down shirt ecru or off-white?

Get a copy of the catalog from www.dharmatrading.com and study it carefully. You will be working with the reactive dyes (these require soda ash and table salt). Be sure to study my article on Fabric Dyeing 101 (link at the top of my column). Remember you will be undertaking an experiment!
have fun,
Jennifer