  We present a comprehensive theoretical study, within a fully realistic
semi-analytical framework, of the photometric properties of early-type
progenitors in the redshift range 0<z<1, as a function of the luminosity and
local environment of the early-type remnant at present-day. We find that,
averaging across all environments at z~1, less than 50 percent of the stellar
mass which ends up in early-types today is actually in early-type progenitors
at this redshift. The corresponding value is ~65 percent in clusters due to
faster morphological transformations in the such dense environments. We develop
probabilistic prescriptions which provide a means of including spiral (i.e. non
early-type) progenitors at intermediate and high redshifts, based on their
luminosity and optical (BVK) colours. For example, at intermediate redshifts
(z~0.5), large (M_B<-21.5), red (B-V>0.7) spirals have ~75-95 percent chance of
being a progenitor, while the corresponding probability for large blue spirals
(M_B<-21.5, B-V<0.7) is ~50-75 percent. Finally, we explore the correspondence
between the true progenitor set of present-day early-types and the commonly
used `red-sequence', defined as the set of galaxies within the part of the
colour-magnitude space which is dominated by early-type objects. While large
members (M_V<-22) of the `red sequence' trace the progenitor set accurately in
terms of numbers and mass, the relationship breaks down severely at fainter
luminosities (M_V>-21). Hence the red sequence is generally not a good proxy
for the progenitor set of early-type galaxies.
