Fruit and veg platters. I used
Veg - tomatoes, carrot, yellow peppe, mange tout, and beetroot crisps.
Fruit - strawberries, small easy peeler citrus, banana, green apples, blueberries and purple grapes
Colouring the cake - I wanted to use as many natural colourings as possible, but I did supplement a couple of them with food colouring. Some sites I used to get ideas are here and here and here.
I think the things I used were as follows
Beetroot juice for Red
Carrot juice and a little beetroot juice for orange
Turmeric for yellow
Spinach juice for Green
Blueberries (cooked and sieved)(and a fair amount of food colouring) for blue (still turned out grey!)
Blackberries (cooked and sieved) and beetroot juice for purple
As you can see, the colours didn't turn out exactly how I wanted them to for a strict rainbow, so I decided to mix up the layers.
Other ideas - pin the tail on the unicorn. We didn't end up having time to do this.
Decorate biscuits - We made biscuits ahead of time and used icing sugar and water and a little food colouring to make a couple of colours of icing, and a bunch of sprinkles (buy from B&M store, if you have one, cheapest place I've found for them!), marshmallows and skittles (taste the rainbow!)
Pass the parcel - the prizes were a colourful notebook and a packet of felt tip pens. I did two parcels with 12 layers each and sent them both round at the same time (I wasn't sure how many kids there would be, turned out to be 18, so some people got a second turn)
Different coloured pots of playdough for game prizes.
Menard printed off some pictures of rainbows, rainbow dash etc and we hung them on thread from the ceiling. And some rainbow butterflies were stuck on the windows. And I got some multi-coloured bunting and hung that. We had paper plates with lots of colours on.
Hope that's helpful to anyone wanting to plan a rainbow party!