Colouring sponge - help please!

[HippoPottyMouth]

I'm attempting a rainbow cake for DDs birthday, and I have gel colours that I have used before in a sponge, but they always end up with a grey colour on the outside - what am I doing wrong?

I did a trial layer the other day to gauge the amount of mix needed for my pan and again, the outside of the cake was a dull grey colour but once you cut it it was a lovely purple. I don't want to have to try and trim the layers or I'll end up with a right mess :(

Unfortunately the cooking of the cake changes the colour on the outside.

I did a thin layer of buttercream on the outside of the rainbow cake I've made.

You need these Any of the colours sold in the supermarkets are wishy washy. A tiny bit of these gives good vibrant colours. Much trial and error here!

Ah, ignore me, completely read the OP wrong!

Yeah it does seen to do this, icing hides it, people won't notice.

Once you slice into the cake, you can't tell it has the discoloured outer layer. There is no way of not getting it, and as others have said, the icing layer hides it

Put baking paper on the bottom and sides and they will stay bright, and cut the tops off. If you are making a six/seven layer cake you really need to level them off anyway, otherwise they will be all wonky by the time you get to the top!

Thanks - I will try the baking paper, also wondering if lemon juice in the cake is affecting it a bit. It's a fairl thick layer, you can see it once sliced so it is a bit annoying. The bottom is the worst.

About to commence first layer so will let you know how it goes!

I have made one of these, and the outside was dull but I covered it completely with buttercream and glitter so it covered it up!

I watched a guy make a red velvet cake with beetroot which looked really bright and no nasty artificial stuff.

I have just done one of these for my ds, 6 layers really thin layer of buttercream between each then 2 thin layer of buttercream on the outside, once cut you done see the dull edges, but you meed the sugar flair or wiltons type gel colours to get the really bright colours.

You have to make a silver sponge - all egg-whites.