  We examine the applicability of effective temperature scales of several broad
band colours to T Tauri stars (TTS). We take into account different colour
systems as well as stellar parameters like metallicity and surface gravity
which influence the conversion from colour indices or spectral type to
effective temperature. For a large sample of TTS, we derive temperatures from
broad band colour indices and check if they are consistent in a statistical
sense with temperatures inferred from spectral types. There are some scales
(for V-H, V-K, I-J, J-H, and J-K) which indeed predict the same temperatures as
the spectral types and therefore can be at least used to confirm effective
temperatures. Furthermore, we examine whether TTS with dynamically derived
masses can be used for a test of evolutionary models and effective temperature
calibrations. We compare the observed parameters of the eclipsing T Tauri
binary V1642 Ori A to the predictions of evolutionary models in both the H-R
and the Kiel diagram using temperatures derived with several colour index
scales. We check whether the evolutionary models and the colour index scales
are consistent with coevality and the dynamical masses of the binary
components. It turns out that the Kiel diagram offers a stricter test than the
H-R diagram. Only the evolutionary models of Baraffe et al. (1998) with mixing
length parameter 1.9 and of D'Antona & Mazzitelli (1994, 1997) show consistent
results in the Kiel diagram in combination with some conversion scales of
Houdashelt et al. (2000) and of Kenyon & Hartmann (1995).
