Chocolate transfers can be made with candy melts. You CAN NOT use icing color (or regular food color) to color candy melts. You have to use "candy color." I know Hobby Lobby sells it; not sure about Wal-Mart. Never seen it there.
Usually I just snip off the corner of my disposable piping bag to do it. Just make sure you cut off the tiniest piece you can, so your line is super small.
To do the transfer:
1. In a word-processing program (I use Microsoft Publisher, but I think Word will work) type what you want to say, like, "Happy Birthday," or whatever. Also make your shape (if you want it outlined in a square, rectangle, banner, etc...) Then flip the sign and wording in the program so that IT PRINTS BACKWARDS. Very important that it's reversed when it's printed out.
2. Tape it to a flat surface (I use a cake circle or cutting board). Lay a piece of parchment paper over the sign and tape it down, too. Make sure your printout and the parchment won't move around. Also, make sure you're piping over the backwards printout. If you can read it the right way, it will come out piped backwards.
3. Pipe over the words with melted white chocolate or white candy melts. Also pipe the sign's outline.
4. Then fill in the sign with a different colored chocolate (candy melts) making sure to cover ALL the chocolate you've already piped. Be sure to cover the entire thing. After you've finished, and while it's wet, tap it lightly to make the back smooth out and to get rid of any bubbles.
5. Once it's dry, carefully peel away the parchment. It should release quite easily. You'll have a finished, clean-looking sign, but only if you've printed it out and piped it backwards. I know I'm beating that horse to death, but I did it wrong once and got quite frustrated!
Hope this helps you. Good luck!