some time ago I saw these enchanting tights:http://theberry.com/2010/01/22/yes-these-are-tights-16-photos/
Now, I finally got around to buying some materials and trying it for myself!
-"expensive" tights (you'll have to stretch and put them on and off a couple of times, so if you take the cheap kind, they'll be ruined before you're even done)
-textile markers (sharpies might work as well)
-rather large piece of cardboard (must be big enough to roughly resemble your leg)
Put the tights on and mark where you want your design to be with a pencil. Be sure to do this on both legs and on the same hight.
Cut the cardboard into a leg-like shape (I used the box my ukulele was in, so I didn't really need to do that)
Carefully but your new cardboard leg (which might come in handy if you turn into a pirate, as well) in one of the tight-legs. Make sure it's not twisted and stretched equally.
If you want to make a straight line, use a fashinable ruler. It helps to keep the tights in place, while you trace your lines. Don't be fooled by the cardboard! Even if it looks black, your tights might not take in enough colour yet, so be sure to go over your lines a couple a times.
If you want to use some kind of pattern for your design, you can either use something to put on top, like I did, and trace it with a pencil (you will be able to see it really well, since you are writing on the cardboard as well) or put a design on a piece of paper between cardboard and tights. If you want to use your cardboard-leg more than once, you can put some paper between tights and cardboard as well.
I used a necklace as inspiration for the details on my design.
Repeat steps 3 to 6 but this time, with the other tight-leg.
Do a happy dance and adore your awesome new tights!
Alternatively you could use a more colourful pair of tights or textile markers. Generally shapes that are not round or square etc. work better, because if stretched, you can hardly notice that they are warped. Keep in mind, that if you stretch your tights TO THE MAX while putting the design on, the colours will appear more vivid, since you have more colour particles in one place. If you do that, don't forget that the design will be much smaller, if you stretch the tights more than your legs are wide.