I made some MMF and colored some of it blue, some of it pink and some of it lavender (using blue and pink). I made it yesterday morning, decorated some cakes, and then when I served it this evening...the color was just about gone! I know that I am working with pastel colors, but it wasn't so "light" that you could barely see the color. The blue remained the same, but the pink and lavender were practically nonexistent! Can someone help me and explain why this happened?

Were the cakes stored in boxes, or out in the open? Sunlight fades fondant . Especially susceptible are colors with red in them...and pink and lavender obviously would qualify. Next time keep those babies in the dark til serving time!

Yes, I put them in a transparent cake carrier which did sit in the sun in the car. Thanks for the explanation. I'm so glad I learned this now on some "samples" rather than the "real" thing. If I had it sitting in the kitchen where this indirect sunlight would it fade, too? How many days in advance should I make the cake then? TIA!

Indirect sunlight isn't much better. I mean, it doesn't have to be pitch black! But on the counter, exposed to the light of the day, could still give you grief. If it were me, I would put it in a cake box, even if you have to prop the box open to fit the cake in (then I'd tape a paper towel or something over the opening) or if you are storing it in your cake carrier, just throw a towel over it to block out the light. You can make the cake as many days in advance as you normally would based on your experience with icing and filling storage. I generally use perishable fillings so I refrigerate nearly all of my cakes...so I don't know too much about countertop storage, although I would say beware keeping it for too many days in an airtight container if you are using that transparent cake carrier, as the trapped moisture may ruin your fondant decorations. To combat that for unrefrigerated cakes, I prop the the lid open with something, to allow air to circulate/moisture to escape.

Wow...thanks so much for all the advice. That is really helpful. I know you have saved me hours of frustration!

Another thing that helps with fading is to paint the red or pink fondant with a mix of icing color and vodka...painted fondant doesn't fade the way that fondant fades when the color is mixed in.

Black will fade sometimes too, so that's another color to watch out for. A lot of times it will fade to green.

While all the above is true the type of coloring also can be the culprit.
When coloring fondant I use AmeriColors, Cake Craft Food Paste, or luster dust. (Beth Parvu colors at sugarpaste.com are great for not fading :0)

I have some red I made a year ago that is still red as the day I made it.. (I use it for teaching classes now).