  We systematically analyze all the available X-ray spectra of disc accreting
neutron stars (atolls and millisecond pulsars) from the RXTE database. We show
that while these all have similar spectral evolution as a function of mass
accretion rate, there are also subtle differences. There are two different
types of hard/soft transition, those where the spectrum softens at all
energies, leading to a diagonal track on a colour-colour diagram, and those
where only the higher energy spectrum softens, giving a vertical track. The
luminosity at which the transition occurs is correlated with this spectral
behaviour, with the vertical transition at L/L_Edd ~0.02 while the diagonal one
is at ~0.1. Superimposed on this is the well known hysteresis effect, but we
show that classic, large scale hysteresis occurs only in the outbursting
sources, indicating that its origin is in the dramatic rate of change of mass
accretion rate during the disc instability. We show that the long term mass
accretion rate correlates with the transition behaviour, and speculate that
this is due to the magnetic field being able to emerge from the neutron star
surface for low average mass accretion rates. While this is not strong enough
to collimate the flow except in the millisecond pulsars, its presence may
affect the inner accretion flow by changing the properties of the jet.
