Here is a link to some helpful info regarding Color Flow:
http://www.wilton.com/recipes/recipesandprojects//icing/colorflow.cfm
with color flow, i just prefer to use royal icing. its not as shiny or tough when it dries but i've never had any problems with it. the reason i don't like to use the actual color flow is because any type of moisture breaks it down. this includes bc so in order to attach the image you'd have to leave the wax paper on and i hate having anything that's not edible on my cake.
is actually really easy. that wilton site makes it sound hard. all you do is...
tape your image to a oard and then tape wax paper over that.
then outline the image with regular royal icing (i use a tip 2 or 3). let it dry for about 1 hour (if you wait too long your outline starts to crack).
to fill in the image, thin out the royal icing with a few drops of water. (the consistency should be like glue) then use that to fill in your image (i use a tip 2 for this). aim your tip towards the outline while you fill in.
you might have some air bubbles and you can use a toothpick to pop those. make sure you do this right after you fill in that particular section since RI does dry fast.
make sure you let your image dry. i usually let them dry overnight.
if you have any more questions you can pm me.
If you dry the royal icing under a reading lamp for 10 minutes or so you get a lovely glossy finish. Try doing a google search on Royal Icing run outs (the british name for this technique) you'll find loads
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