Could get some color into the cake by macerating strawberries in a cake recipe's entire sugar quantity. Strain and weigh the resulting liquid. the additional liquid has to be subtracted from recipe too.
Problem there is that sugar is a good flavor vehicle...
Tomato? There are those crazy old-fashioned red velvet cakes. Could also try beautifully ripe red bellpeppers (chilli peppers work too, ouch) either as a puree or used to stain the recipe's fat/oil/butter.
Nothing above is even close to commercial colors in that consistency or flavor is influenced but maybe you will find a combination that satisfies you. I'm still looking for a natural orange for kids Halloween!