Selection of new CTTS candidates from the (g − r, u − g) diagram. The gray dashed line traces a conservative boundary separating the accretion-dominated region of the diagram from the color locus of non-accreting stars (see text). Field stars, WTTS and known CTTS are depicted as gray dots, blue triangles and red circles, respectively; the new CTTS candidates selected from this diagram are marked as green crosses. The purple line fitting the upper envelope of the WTTS distribution traces the reference sequence of photospheric colors that has been adopted for measuring the UV excess of accreting stars (see Sect. 4).