  We use multi-wavelength data from the Galaxy and Mass Assembly (GAMA) survey
to explore the cause of red optical colours in nearby (0.002<z<0.06) spiral
galaxies. We show that the colours of red spiral galaxies are a direct
consequence of some environment-related mechanism(s) which has removed dust and
gas, leading to a lower star formation rate. We conclude that this process acts
on long timescales (several Gyr) due to a lack of morphological transformation
associated with the transition in optical colour. The sSFR and dust-to-stellar
mass ratio of red spiral galaxies is found to be statistically lower than blue
spiral galaxies. On the other hand, red spirals are on average $0.9$ dex more
massive, and reside in environments 2.6 times denser than their blue
counterparts. We find no evidence of excessive nuclear activity, or higher
inclination angles to support these as the major causes for the red optical
colours seen in >= 47% of all spirals in our sample. Furthermore, for a small
subsample of our spiral galaxies which are detected in HI, we find that the SFR
of gas-rich red spiral galaxies is lower by ~1 dex than their blue
counterparts.
