i want my white cake to be as white as the picture on the box. any tips??

are you using egg whites and not whole eggs?

If you are trying to achieve a cake that looks like the photoshoped picture on the box, you will constantly be dissapointed. Packaging is made to be enticing. They alter the foods in order to achieve a " picture perfect " product. If your using egg whites only, it's as "white" as it can be. Perhaps you should bake a white cake and a yellow cake, cut them in half, place them side by side and marvel at just how white, your white cake really is!

I use the wilton White colouring

Are you adding anything to your mix...pudding, vanilla, even the oil is a little yellow. All those can alter the color a little. Do you think people are looking at your cake wishing it was more white? Or is it just personal preference. If so, don't be so hard on yourself, as long as it tastes great, no one will mind the hint of cream I'm sure

Is it just the mix the way it is on box or do you use extenders or additions?