6 December 1906
The Transvaal Colony, former Zuid-Afrikaansche Republiek (ZAR) or Transvaal Republic, was granted self-government status by Britain, according to the terms of the Vereeniging Peace Treaty, signed between representatives of the two Boer Republics and Britain on 31 May 1902. The implementation of this term was precipitated by the replacement of the Conservative government in Britain by the Liberal administration in 1906. Transvaal was followed by the Orange River Colony in 1907.    One of the clauses of the Vereeniging Peace Treaty (1902) gave the White people in the conquered Transvaal and the Orange Free State the right to decide whether or not to extend the parliamentary franchise to Black South African's. The Boers decided not to, and Blacks were excluded from the vote.
References

Kruger, D.W. (ed)(1979). Geskiedenis van Suid-Afrika; verwerk en bygewerk deur D.W. Kruger; 3de bygewerkte uitg., Goodwood, Cape Town: NASOU, p. 457.|Wallis, F. (2000). Nuusdagboek: feite en fratse oor 1000 jaar, Kaapstad: Human & Rousseau.|Oliver, R. and Atmore, A. Africa since 1800. google books online. books.google.co.za