I can induce SP, and feel my body going numb, and occasionally I see colorful patterns on my eyelids, but I can never "enter" a dream.
Hi 182!

If you really can induce the SP, then all you have to work on crossing over that threshold which allows you to pull in your consciousness with you. Think of the colorful patterns and all as the 'dream' part of you, and the paralysis as your 'awake' or 'real' part of you. Imagine there's a wall before you which moves from side to side depending on whether you're mostly in 'dream' mode, or 'awake' mode. In this wall there is a small gap, just wide enough for 'you' to fit through. This gap lines up directly in front of you ONLY when you are in perfect balance between dream and waking.

V---------------------------------WALL---------------------------V

<--dream---------------- GAP(balance) ------------- awake-->

So, the object is to get that 50/50 balance, step through the gap, and be in a lucid dream!

My guess is that once you start seeing the patterns, you're gettin anxious about entering a dream lucidly (happens to most people, including me). So, what you have to do is let go a bit - LET it happen. You risk falling to sleep, but if you get too anxious you also risk killing the entire experience and waking up completely. Frustration will make it even more difficult to fall back to sleep.