  We present colours of sources detected with the Herschel/SPIRE instrument in
deep extragalactic surveys of the Lockman Hole, Spitzer-FLS, and GOODS-N fields
in three photometric bands at 250, 350 and 500 micrometers. We compare these
with expectations from the literature and discuss associated uncertainties and
biases in the SPIRE data. We identify a 500 micrometer flux limited selection
of sources from the HerMES point source catalogue that appears free from
neighbouring/blended sources in all three SPIRE bands. We compare the colours
with redshift tracks of various contemporary models. Based on these spectral
templates we show that regions corresponding to specific population types and
redshifts can be identified better in colour-flux space. The redshift tracks as
well as the colour-flux plots imply a majority of detected objects with
redshifts at 1<z<3.5, somewhat depending on the group of model SEDs used. We
also find that a population of S_250/S_350<0.8 at fluxes above 50 mJy as
observed by SPIRE is not well represented by contemporary models and could
consist of a mix of cold and lensed galaxies.
