I need to made purple fondant next week for my daughter's Rapunzel Tower birthday cake.

Today she and I were mucking around decorating cookies with royal icing and I decided to have a practice with the colours, thinking it would be straightforward. But no - I mixed a little natural red liquid food colouring and a little blue into my white royal icing - and it went grey instead of purple! What am I missing?! I'm trying to save money and use what I have, but am I going to have to buy violet colouring? I need a couple of different shades too!

Yeah, I never get purple without actually using violet or lavender coloring. Or even just buying lavender fondant. Maybe someone else has a secret, but I always hit that roadblock, too.

I make my own purple/lavender colors all the time and I use that same technique, Mixing red and blue. but like we were taught in grade school doesn't work exactly that way with fondant or icings. First I make my frosting or fondant blue and after it is well blended in I add the red to get the shade/hue I want. If you use red first you have to add the orange to get the red so that's why I use blue first. The deeper the blue the deeper the color purple.

HTH

I just finished making lavender for ribbon & bows for todays cake. Came out perfect.

auntginn, I'm confused on why you need to add orange to get red....
On the grey thing, it might be your red; all reds are not created equal. What are you using? I like the Americolor super red. If you have an orangey red, that could be adding the yellow that would turn the purple grey. (If you mix purple and yellow, you will get a grey) That is why some people add a dot of purple to their buttercreams that have a large amount of butter in them. It neutralizes the yellow from the butter.

The ph balance of your fondant is off. Add a pinch of baking soda to your fondant, then add your colors and it will help. Purple is really hard to get, but the baking soda will solve your problem.

She also said she was using liquid food colors. Use gels! Americolor is sold at Hobby Lobby and it's better than Wilton...but even Wilton gels are better than liquid.

Its best if you get a color wheel to understand colors. But if you have fondant already colored you can use this chart from Satin ice.
Remember everyones monitor is different and may vary.

I missed the royal icing part, I thought she said she needed to make purple fondant. Well, can't help with the royal, that should be no problem.

I've mixed pink and blue before to get purple, after having the same problems with blue and red.
That might help.

I also use pink and blue to get purple.

Thanks you all sooo much for all the replies! I suspect the red colour is the culprit, I was using Dr Oekter natural red liquid colouring, and it was a weird texture, kinda gloopy? Both my red and blue colours are brand new and bought this week from the supermarket, so don't think it had gone bad, but I suspect the natural red was not a "true" red, as someone mentioned in their reply. I'm going to try a test with colouring a little fondant red then adding blue, if that doesn't work I'll be off to buy new colours.

I'm only just getting into this cake making lark, so still using amateurish colours - definitely need to get into using gels if I'm going to do this properly! Thanks again everyone!

I agree with stepOnmi, supermarket colors are #1 not concentrated enough for the use and #2 usually contain too much water which will make the fondant very sticky.

When I make red, I first add orange to fondant or icings to break up the white, then add the red. This way I will get red and not pink. (red & white = pink even if you add a lot of food coloring)

Update - tried adding the red to blue fondant, still got grey - definitely must be a dodgy red. Have got along OK adding liquid colour to fondant so far, but this is the end of that road I think! Off to get gel colour this week then!

Thanks again to everyone who took time to help me!

SUCCESS - I HAVE PURPLE FONDANT!

To the person who suggested mixing pink and blue - thank you! I got a bottle of pink liquid colouring and mixed a little of that and a little liquid blue, and it worked and I can now get the various shades I want. I know you're not meant to use liquid colouring with fondant, but I have found it works fine as long as your not using too much liquid (kneading a little icing sugar in thoroughly can correct any stickiness in my experience). Nonetheless, I also bought red and blue gel colours at the same time, and they definitely get a more intense colour - not needed in this project, but with a little boy who's favourite colour is red, I can see a use further down the line...

Again, thanks for all the replies!

AI have been dabbling in decorating cakes and I also work at Home Depot in the paint dept. I can also add that from what I have learned, mixing paint ( for 10 yrs). Colorants behaviors very greatly depending upon the formulation of different paints. The same formulation in Behr brand paint will not result in the same color in Glidden. I can tell you that in order to get darker reds and true purples the colorant added is magenta. The closest in say Wilton is the rose color.1 more thing to add in paints we have different bases which help..1. White base is pure white with lots of Titanium dioxide, ( for light colors).2 pastel base with about 25% less white for pastels.3 Accent base almost no white, for darker colors. 4. Deep base, with no white in it, it is basically clear, for pure colors and blacks. In fondants, frostings ,icings we are fighting to hide whites and some of those are a bit grey and ivoryish themselves.

The best thing that has helped me learn a lot is scouring the internet and learning how we perceive colors.. Also make sure your lighting is accurate color rendering bulbs.

I could go on and on... But instead if anyone has questions just ask..

Usually if that happens you used too much of one color. Usually you need more red food coloring then blue to make purple. You might have used the same amount for both.

That looks awesome!  I'm always up for a heavy read when it comes to cake! Thanks for sharing.