This can be done with plastic or stemware. Given the circles I entertain typically involve large amounts of children, I often choose the nicer plastic glasses with the "crystal effect".
And sanding sugar, available at most craft warehouses or specialty cake shops, comes in a variety of colors. You can do several colors, or even mix sugars for an added dimension.
Sanding Sugar (color of choice)
Lemon Juice or Water
*Note: You can use water instead of lemon juice, but I find lemon juice to adhere a bit better to the sugar. Feel free to experiment with this. Also, only in the specialty cake shops did I find sugar actually labeled "Sanding Sugar". Any colored sugar should work. However, if the granules are too large, you will have trouble getting them to stick to the glass.
Put water in a bowl, to the height you want the rim to be on the glass.
(Water height will determine thickness of rim.) Pour colored sugar into bowl, deep enough to dip the cup rim past the water line.
Dip the cup first into the water bowl.
Next, dip the cup into the colored sugar bowl, making sure to twist, and ensuring that sugar is on both the outside and inside of the cup rim. As you pull the cup up from the sugar bowl, give it a couple of shakes to rid of excess sugar, and store upright to dry for at least an hour before using.
Now, as you can tell from the next picture, you will need to keep a watchful eye on any children assisting you....at least if you plan to serve the cups for guests!
Also, for the benefit of your party guests, we will include the following demonstration:
Once the sugar becomes wet from liquid, the color can seep out....especially if the cups have not had time to properly dry. If it has plenty of time to dry, it doesn't bleed a lot, though some colors seem to do this more than others. You can also choose to do just a partial sugar rim.
So, if you don't allow the sugar to dry long enough.....or find your guests are drinking as follows:
Their faces may then resemble the below:
Or, you can always suggest they drink like this: :-)
Seriously, however, colored sugar rims can greatly impact the visual display, with little added cost or time. The below pictures are from a friend's 50th Birthday celebration....they mixed purple and pink sugars and dipped the stemware (no this is not plastic) in water. The effect was stunning.