I can't imagine that whipped eggs baked with other ingredients could have enough residual sulfur to cause a color change only to the top of the cake two days later.Now I am wondering if it is the diet of the hens that laid those eggs. I can imagine that if there is a lot of sulphur in the food they eat that it could turn the yolk part of the eggs greenish. When you hard boil eggs, do they often get a greenish or greyish ring around the yolk?
Every time i use WHOLE EGG whisking and egg separating whisking method, my cake always starts to turn the color from nice yellowish to some greyish color on top.
What is that? It doesn't taste moldy, nor it smell funky. Taste all the same