So, why do your once sunny yellow egg yolks sometimes turn a shade that’s more reminiscent of a leprechaun’s favorite color? The answer is all about the way you cook those eggs. You see, the culprit behind this intriguing transformation is none other than heat – more specifically, eggs being cooked for too long and/or at too high a temperature. The Ideal Yolk Color Okay, so we’ve tackled the green yolk situation, but what color should a hard-boiled egg yolk actually be? Ideally, it should have a rich, sunny yellow hue. This color indicates a perfectly cooked egg with a yolk that’s both visually appealing and deliciously flavorful