This "mold" won't scrub off...is it something other than mold?

[Jack B.]

Tenant moved in and said there is mold in Washer. I go to take a look and scrub it off with a bleach and baking soda paste. First wipe it with a paper towel and bleach and NOTHING comes off. It's completely clean. SO I use the bleach and baking soda paste with a scouring pad and scrub for a long time, even let the solution sit on it for a while. Nothing comes off. Some of the stains are dark some are yellow. What is this? I bought a mold test kit, I will go there and test it but I'm starting to think this is NOT mold. But what is it? Some of the stains are dark and some are yellow. And how should I proceed from this point? Liability worries me....she has a baby...