I need to do a snail trail around the bottom of a ivory coloured cake but am not sure exactly what colour to use to match the ready made 'plastic' icing.

For Ivory royal icing i normally add a very tiny amount of beige colouring to the white royal icing

thanks i will try that!

you can actually buy ivory color if you have the time otherwise a dash of tan or light brown or beige will do the trick

I use brown with a touch of yellow

I use a teaspoon of brown vanilla to a pound batch of royal for ivory.