Custard powder is primarily made up of thickeners that give the pudding its texture. Cornstarch is usally the biggest component, since it is great for thickening liquids, disolves easily and is almost foolproof. The powder also contains flavorings – vanilla is the one you’re most likely to find in a “standard” custard powder – and a hint of yellow coloring. Yellow coloring gives the custard just enough color to look as though there are plenty of eggs in it, as most basic custards are thickend with eggs instead of powder.