I noticed this in some car park toilets in Bournemouth recently and when I asked about it the friendly operative told me that it is to discourage intravenous druggies from using the toilets as under those blue lights they can't see the veins to stick the needle into.
Yep, that's the reason. If it's a serious drug area, you will see that the tops of the toilet cisterns have been removed as well, to avoid offering a flat surface for people to set out their drug pariphenalia (sp?).