I am new to cake decorating and have never used fondant. I found a cake design I want to make for a baby shower and it is covered in fondant. It also has fondant people on top. I am a little intimitated by all the fondant. Could you put the fondant people to a cake frosted in buttercream? Also, what is the best way to color fondant?

Most people do put buttercream under the fondant because you need something for the fondant to stick to. Others may use glazes, etc.

The best way to color fondant is to put on some gloves (you hands will get dye on them), and add a little color at a time and knead it in. I use Satin Ice but for those who make their own marshmallow fondant will add some of the dye while making the fondant. The only thing to be careful is that you may add too much.

Edited to add:
I misread the question, I thought the OP was asking if you can put a fondant covering (not the people) over a buttercream cake.

I use a crusting buttercream, and when I add fondant accents to a cake I slightly wet the buttercream where the fondant will be placed.

Sure - you can always add fondant accents to a cake that is mainly covered in BC.

You can color fondant by just kneading some gel color into it. It will look marbled at first, but just keep kneading. To keep the color off your hands, some people wear gloves but that does not work for me. I just rub some shortening over my hands, sort of like lotion but not totally rubbed in, and add a few drops of gel color into a blob of fondant and start kneading. Works great - the gel color won't stain your hands and that small amount of shortening doesn't alter the fondant consistency much, if any.

If you have a large batch to color, you may want to color a smaller portion first, then knead it all into each other. Remember, the smaller portion's color will lighten up when added to the remaining uncolored portion so if you use this method, make sure to color the small batch darker than you want it to be.

You should be able to attach fondant accents to buttercream, but if you use a crusting BC, you should use something to attach the fondant. I like to use piping gel, but I'm sure there are other options.

As far as coloring it, I most of us just put the gel colors in it with a toothpick (or something similar) and then knead it until it's blended throughout. I know some people, if making their own MM fondant, add the color to the melted marshmallows. Good luck!