I have done many cakes in lots of different colors....I have a customer now that wants a lemon cake (and mine are a pale yelllow) but they want the cake to be a bright blue color....I have tried a couple attempts and it still looks a green.....Can anyone help or am I out of luck.....Thanks in advance for any help....

I would use a white cake recipe and add lemon extract to it (in place of the vanilla). I'm guessing the light yellow is coming from lemon zest, lemon juice and also egg yolks and butter. A true white cake recipe will use only egg whites and often vegetable shortening. To add a little more lemon flavor try filling with lemon curd (so yummy!) The blue color should come through nicely with the white cake. Hope that helps. Let us know how it come out.

This was my next option.....I make a really good lemon cake but the customer is adament about the inside being blue but with a lemon cake......Thanks alot.....

But ALSO ..... explain the basic science.  Blue is a primary color and cannot be created.  Therefore the things that make your cakes so luscious is the YELLOW butter, the YELLOW eggs, the YELLOW lemon .... and no matter how you mix it, yellow + blue = green.  It's science.  It happens.  PIck one.

What indydebi said.  Can you cover with blue fondant?