Chicken egg color turns brown with water! Can write name.

My brown egg turned white, but I noticed where my moist hand was, it went brown where I touched it. I got an idea, use an applicator, eraser or anything get it wet and wrote my name! Have gotten 2 like this.
Anyone explain this? Rhode Island Reds. Only hens. Thanks! Sandy

The colour is added as it is laid, hence why inside it is white. Legbars with coloured eggs, the colour is added as the shell is made hence the inside is the same colour as the outside