We study the globular cluster (GC) system of the Virgo giant elliptical galaxy NGC 4365, using new wide-field VIK imaging.
The GC colour distribution has (at least) two peaks, but the colours of the red GCs appear more strongly weighted towards
intermediate colours compared to most other large ellipticals and the integrated galaxy light. The intermediate-color/red
peak may itself be composed of two sub-populations, with clusters of intermediate colours more concentrated towards the centre
of the galaxy than both the blue and red GCs. Nearly all intermediate-colour and red GCs in our sample show an offset towards
red V-K and/or blue V-I colours compared to SSP models for old ages in a (V-K,V-I) diagram. This has in the past been interpreted
as evidence for intermediate ages. We also combine our VIK data with previously published spectroscopy. The differences between
observed and model colour-metallicity relations are consistent with the offsets observed in the two-colour diagram, with the
metal-rich GCs being too red (by about 0.2 mag) in V-K and too blue (by about 0.05 mag) in V-I compared to the models at a
given metallicity. These offsets cannot easily be explained as an effect of younger ages. We conclude that, while intermediate
GC ages cannot be definitively ruled out, an alternative scenario is more likely whereby all the GCs are old but the relative
number of intermediate-metallicity GCs is greater than typical for giant ellipticals. The main obstacle to reaching a definitive
conclusion is the lack of robust calibrations of integrated spectral and photometric properties for stellar populations with
near-solar metallicity. In any case, it is puzzling that the intermediate-colour GCs in NGC 4365 are not accompanied by a
corresponding shift of the integrated galaxy light towards bluer colours.