Covid-19: For updates and resources, head to UT's Protect Texas Together site.
Rather than supplanting the Bluebook, the Greenbook supplements it with regards to citation issues that are unique to Texas. Where the rules conflict, you should follow the Greenbook when citing Texas authorities.
Most citation in the Greenbook follows Bluebook style. Below are some notable features from the Greenbook about Texas citations.
Texas Law Review offers the GREENBOOK and MANUAL ON USAGE AND STYLE through the Rulebook App.
Go to https://texaslawreview.org/ordering/. Use the 'Rulebook App' download on the bottom right.
Both titles are also available at Amazon.com, and orders can be placed through TXShop (https://utdirect.utexas.edu/txshop/list.WBX?component=0&application_name=LOLSPUBS&cat_seq_chosen=04&subcategory_seq_chosen=003).