I had some people ask about a tutorial for my intergalactic nails, so I threw together a super quick one that should give you a basic idea. I have a terrible camera, so I apologize for the photos, but I hope it helps!
You will need various nail polish(mine are listed in my previous post), a makeup sponge applicator, a small brush or toothpick, and a palette to put the polish on(I used a paper plate).
To start, I chose a dark base. You can use dark blue, black, purple, whatever you want. I chose DS mystery because it has a nice sparkle to it. I did two coats and let it dry completely.
Next, take the sponge and apply a small amount of pale or baby blue, gently dabbing it onto the nail in whatever pattern you want until you get the coverage you desire. Remember to be gentle and keep a light hand.
Over the blue, I applied a spring green using the same dabbing technique.
Over this, I next applied pink/magenta. Experiment with different colors. Purple also works well! I like this pink because it has a faint blue sparkle to it.
Next, I apply a little yellow. It turns a bit orange-ish when applied over the pink, which is fine. Concentrate it in certain areas if you desire to make them brighter.
You can't tell, but I applied a sheer orange shimmer over the yellow/pink areas for a little depth and shine.
Next, I took a darker, more royal blue and dabbed around the edges of the 'nebula'. You can use it to help shape and darken areas in.
After that, I used more of my base color, the dark violet, so do a little more shaping/darkening of certain areas. Just gently dab it around until you're satisfied. I also added in a touch of Orly's Space Cadet on the dark areas, which give a nice additional space-y shimmer.
Last, use a small paintbrush/toothpick/whatever to add some 'stars' randomly. I then add some sheer holo-y glitter to the nail, not all over it, just in random spots. Slap on a topcoat and that's pretty much it!
I did this super fast so I didn't do much shaping, but it gives you the general idea. Have fun and experiment with it! Use different colors, patterns, whatever! It's mostly trial and error. I hope this was a little helpful to some people. :)