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We use our integrated SDSS photometry for 96 globular clusters in $g$ and$z$, as well as $r$ and $i$ photometry for a subset of 56 clusters, to derivethe integrated colour-metallicity relation (CMR) for Galactic globularclusters. We compare this relation to previous work, including extragalacticclusters, and examine the influence of age, present-day mass functionvariations, structural parameters and the morphology of the horizontal branchon the relation. Moreover, we scrutinise the scatter introduced by foregroundextinction (including differential reddening) and show that the scatter in thecolour-metallicity relation can be significantly reduced combining tworeddening laws from the literature. In all CMRs we find some low-reddeningyoung GCs that are offset to the CMR. Most of these outliers are associatedwith the Sagittarius system. Simulations show that this is due less to age thanto a different enrichment history. Finally, we introduce colour-metallicityrelations based on the infrared Calcium triplet, which are clearly non-linearwhen compared to $(g^\prime-i^\prime)$ and $(g^\prime-z^\prime)$ colours.

G2C2 II: Integrated colour-metallicity relations for Galactic Globular Clusters in SDSS passbands