I am making a babyshower cake for a lady at work and am trying to acheive a color of fondant that I am unsure what colors I should mix together to reach. The base cake is going to be a pillow cake with "celery sprig" fondant. Any suggesstions on this? I am thinking yellow, green and possibly a tiny bit of black? Or maybe just yellow and green?

That almost looks like an Avocado green from americolor...I would add a touch of yellow though..start with a soft green like avocado.

Is there something other than a computer screen you are trying to match a color to?? Because looking on a screen only could possibly make the color you make very different from the color the customer wants. That is because a computer screen shows different colors than what is real. My screen could should a lime green color while yours could show a much darker forest green color. I am the yearbook advisor at the high school I work at and they tell us to not base what the book is going to look at by looking at a screen. I am very glad because the red we are using (our school color is red) looks very pink on the screen. But in the color guide book it is a much darker red. Anyways, the point is, I would make sure I have something like a napkin that is going to be used at the party to match to.

Back to topic, based on the color I see on the screen, I would say use green, maybe a little yellow, and a tiny bit of brown. I wouldn't use black, it looks more like brown to me.