I would think so, I just made some very blue (not quite Royal, but close), using Wilton's Royal Blue. Are you making the fondant or is it already made? It will take more color, if it's already made. If you are making it, put the color in while you are making the fondant. I make MMF & put it in when I' stirring the marshmallow soup.
It works great!
I think so! I did this cake (link below) with MMF and Wilton colors. Like the poster above, I mixed the colors in with the marshmallows when they were soupy. Lots and lots of blue and a bit of black for this shade.
Good luck!
http://www.cakecentral.com/modules.php?name=gallery&file=displayimage&pid=75190
Quote by @%username% on %date%
%body%