I am wanting to do a carrot cake for my boyfriend's birthday in the next month or so but I know that he also likes the 'rainbow style' cakes, a different colour in each layer. I am curious as to whether the americolour food colouring pastes would be good enough to give the cake a vibrant colour without tasting off? For yellow and orange I would be willing to just do a white cake to get the colour bright enough but would only do this as a last resort.

Thanks in advance!

Have never attempted anything like that but remember a carrot cake has a brown color base so getting vibrant yellow or orange is not going to work - well, the orange might but definately not the yellow
I would say Americolor pastes/gels would work fine. I never had them give an off taste to my icing.