I think you can but you would have to let each color/sanding sugar dry completely before applying the next color/sanding sugar. (I always use the same color of royal icing as sanding sugar I want to use) If I am doing a striped cookie and want to use different colored sanding sugars, I apply one color, apply the sanding sugar, shake off excess and then let dry completely. Then I would repeat the same process with each color.
Thanks VanGough. Before yankeegal answered I was seriously thinking people must make stencils to apply them so close together almost like dusting a cake with powdered sugar. It sounded like so much work that I've never tried it. I'm glad it's just a simple solution.
Bakinccc, I know exactly what you mean about the stripes and the sanding sugar mixing into the next color. I've never been good at it. I'm gonna try the hints here but I was also thinking about it and trying to come up with a remedy. What if you (assuming the line between each color is straight) take a piece of paper and hold it over the line to separate the colors. That way no sanding sugar will get on the "other" color and be hard to remove. Do you understand? I mean to use the paper as a shield or a barrier between the two. Does that make sense? Just tryin' to help!! 
Peeverly - I get what you're saying and that's what I thought of first if I were just to do straight lines, but the designs I have in mind are more curvy. I'll just have to try applying one color at a time letting each dry in between. Hope it works and thanks for the input!!!!!
Well here's one of the cookies I did with the sanding sugars applied right next to each other. Thanks to everyone's advice here I did it for the first time with these "Joseph" cookies and they turned out great.
A lot of people are asking how I did them so I thought I'd post it on here. I first did the outlining in black one day and let that sit overnight. The next morning I attacked the coloring. I would fill about 10 of the red sleeves with icing then go back to each one to apply the red sanding sugar, tap off the excess, then use a clean "blush brush" from any make-up department (mine is only used for cookies) to brush off the stray sugars that stick even after tapping it off. After doing the 60 cookies in red I went back to the first ones to do the orange icing/sugar and was pleasantly surprised to see that the red was dry enough that the next orange sugar didn't stick. No stray orange sugars stuck to the red sugars although there were a few orange crystals on the remaining unfrosted parts of the cookie so I brushed them off again and repeated this whole process with the rest of the colors. It took me 4 hours to do all 60.
So if you were only doing a few cookies that would translate into about 45min drying time for one color before moving onto the next. Much quicker than I expected.
All that sanding sugar over the entire cookie made it taste a little sweeter than normal but I LOVE a sweet tasting cookie so I didn't mind a bit. 
It was my first time covering an entire cookie with all these sanding sugars. I charged my normal charge for them because the customer wasn't even expecting me to do that but it's Joseph's colorful coat...I just HAD to do it!! I would definitely charge more for this extra touch in the future!!
Thanks for the many nice compliments on these cookies!!!!!!
it looks amazing. did you have any trouble piping the lettering over the sugars?
Hi Dawn!!!!!
That's a good question because the lettering caused me the greatest amount of stress!
When I did the lettering and the little shading lines occasionally they wouldn't stick because there was a little loose sugar on the cookie. So I'd have to lift that line off and reapply it. But it would always stick on the second try. That only happened about 5 times in all 60 cookies. I learned you really need to make sure you tap off all excess sugar.
Then the next morning after they dried I looked at them again really close and noticed that the lettering almost looked like it was simply set down on top of the sugars. (Oh my gosh!!! What if my writing didn't stick securely???!!!) I was thinking that I'd have lines breaking off all over the place when I packaged them. But not one line was lost. Whew!!!! So you'd need to make sure your piping icing is just thin enough to sort of "sink in" to the sugars but not too thin that your lettering melts into blobs.
Have you piped over sugars before? Can you relate?
yes, that's why i asked. i was so scared of how they would look a couple hours in the bags.
well, your cookies look fabulous. you're still my favorite cookie decorator!!
i know i haven't posted anything new in awhile. between my kids stealing my camera and being so stressed trying to find a new kitchen. maybe this week i'll have some "free time".
Is it possible to apply one color of sanding sugar right next to another color of sanding sugar without getting the two mixed? I have some detailed designs in mind where I would want three colors of sugars covering the whole cookie. Any ideas?
I agree with the others, apply one color, let dry completely and then do the next color. Keep a small brush handy to brush off the new color off the old color (it won't stick if the old color is dry.) On my www I have a cookie that was designed to look like Gilda Radner and that bad boy takes three days to make just in drying time! 
Is there a trick to putting sugar on the cookie. When I put the RI on and then put the sugar on it ran all down the sides of the cookie 
So after a couple of cookies did this I flooded the cookie and let it sit for a minute before adding the sugar. Is that the right way to do it? I didn't use and outline on the cookie so I was thinking that might have been why they ran 
nickshalfpint - there are tricks to applying the sugars but you're definitely on the right track. When you apply the sugars it makes the icing heavier which makes it want to run more. So an outline helps a lot...sort of creates that edge needed to keep the fill icing in place. If you don't do an outline then letting your icing dry for a few minutes should help hold it in place...and your sugars will sparkle more because the sugars sit more on top of the icing rather than sinking in so much.
thanks to everyone else for the nice comments!!!!!!
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