Art. 448  from Oldham and White (1859), 120, also gives a standard for racial definition.
George W. White and Williamson S. Oldham, eds. A Digest of the General Statute Laws of the State of Texas (Austin, Tex.: Printed by J. Marshall & Co., 1859), 120 (link).
Witnesses, who are incompetent.
Art. 448.  All Negroes and Indians, and all persons of mixed blood, descended from negro ancestry, to the third generation inclusive, though one ancestor of each generation may have been a white person, shall be incapable of being a witness in any case whatever, except for or against each other.[b]
- [b]Negro testimony is inadmissible in all cases, except for and against each other. Rice v. Lemon, 16 Tex. Rep. 593.↩