These are the Betty Crocker gel colors in a tube, in a box that I talked about:
I mentioned them because they're readily available at grocery stores.
The Wilton colors come in small pots with screw off caps. Some are gel and some are paste. They come in a wider variety of colors and they're more expensive because each pot costs over $1.
With either one, you add them to your fondant, buttercream, cake mix, etc. to get the color you need. With the tubes, you squirt it in and with the pots you add it using a toothpick or knife tip--never put either one back into the pot of color until it's been cleaned or you'll contaminate the color and have to throw it away.
How much you add is up to you and depends on the color you need. Dark colors are hard to obtain without getting a funny taste.
Glad to be of help