Probably your retina switching from dark/dim vision system (rods) to bright light system (cones). Not likely to be a sign of trouble.
I have been having the same thing happen. Upon waking from a daytime nap every thing is a strong green colour (like I was looking through green sunglasses) which lasts a few seconds and goes after I blink, really weird. Im on Venlafaxon so Ive put it down to it being a side affect of it.