Hi Hugh, though I find your theory, well, a bit stretched (to use a euphemism), I am conquered by your spontaneity and sympathize with you sleeplessness, hence I'm willing to play along. Here's my contribution: on the other hand the sleep-inducing glass of hot milk or cup of chamomile tea are light coloured. Have a good night!

Hi Layla,
It's funny as I actually wrote that originally (the milk part) but then decided to delete it. You see the theory didn't seem to exactly work with it, at the time. (I was tired and delirious but it still needed to make sense). Because if black drinks invite you to be awake in darkness, whenever you drink them, light drinks should have invited you to be awake during the day, whenever you drink them. But now that I rethink it, the inversion makes more sense and light colored drinks should put you to sleep during the day, but not if you drink them at night. (By night I mean after 2AM).
Rethinking it, it seems to me that when drinking milk at night it doesn't put me to sleep, only during the daytime. Hence, the theory works. Thanks.
Water is I guess like Switzerland - colorless and objective.