I tested 8 colors of the Frixion pens and 5 colors of the Frixion highlighters.
With the pens, I had to scribble pretty hard to get lines on a white-on-white print fabric. They disappeared instantly when I ironed them.
The highlighters left a white mark when they were ironed, with a trace of color. All the marks came back strong when I put them in the freezer.
But, all the marks disappeared completely with just a few seconds of hand-washing in cold water with a little Dawn dish soap.
Next, the Crayola washable markers.