I've also heard of going back to blackness before entering your dream; how do you know that you've just closed your dream eyes instead of just going back to where you started?
Yes the blackness problem can and does occur. The best way to figure it out is to perform a RC (reality check) that does not require you to move very much at all (moving to perform a RC would ruin your progress, if you're not yet in a dream).

There are two RCs I've heard of that are useful in this case.
A) You try to stick your tongue through your teeth. If you can, you're dreaming

B) You block your nasal passage with the muscle at the back of your throat. If you can breathe through your nose, you're dreaming! (Hard to explain what muscle this is—but when you swallow, this muscle will always automatically block your nasal passage so you can't breathe through your nose. That's the muscle to use).

I will also add, that in my own personal successful WILDs I have never seen any colors to any great degree, and have never seen images at all. I usually do hear a very loud sound in my ears right before transition; this is called tinnitus. At this point, I usually just "know" that I can move my dream body without moving my real body (I can't feel my real body at all at this point), and I just roll off my bed or stand up beside it (in my dream body). When you get this far, make sure to use stabilizing techniques so you don't wake up.