Custard powder is often coloured with a blend of tartrazine yellow or quinoline yellow food dyes, mixed with sunset yellow. In solution with water, these colours are true to their names, but in their pre-dissolved solid phase the sunset yellow portion is more orange-red, and this colour tends to dominate.

What colour should custard be?

Custard is a distinctive creamy yellow colour and can range in thickness from a single cream pouring consistency to a thick, spoonable sauce.

Why is custard so yellow?

It's mostly a starch that has been coloured yellow, sweetened and flavoured so that when hot milk is added the starch will make not only thicken the liquid, as a starch is bound to do anyway, but to give it the right colour, taste, and aroma for a custard-like sauce.