  Phase differences and amplitude ratios at different colour photometric bands
are currently being used to discriminate pulsation modes in order to facilitate
mode identification of kappa-driven non-radial pulsating stars. In addition to
physical inputs (e.g., mass, T_eff, etc.), these quantities depend on the
non-adiabatic treatment of the atmosphere. This paper presents theoretical
results concerning Delta Scuti pulsating stars. The envelope of each of these
stellar structures possesses a convection zone whose development is determined
by various factors. An interacting pulsation-atmosphere physical treatment is
introduced which supplies two basic non-adiabatic physical quantities: the
relative effective temperature variation and the phase lag phi^T, defined as
the angle between effective temperature variations and radial displacement.
These quantities can be used to derive the phase differences and amplitude
ratios. Numerical values for these quantities depend critically on the alpha
MLT parameter used to calculate the convection in the envelope. The dependence
on alpha was analized and it was found that the use of colour observations may
be of considerable importance in testing the MLT. Finally, examples are given
of how alpha introduces uncertainties in the theoretical predictions regarding
phases and amplitudes of photometric variations in Delta Scuti pulsating stars.
