We had a leaky toilet (2nd floor) that was repaired but now there are yellow and grayish blue stains on the vinyl floor. I thought it was mold but our contractor says it's not. The subfloor is not soft. He wants to install a new floor over the top. I cut a little piece of the vinyl and it was a grayish green powder beneath even though it appears blue above the vinyl. I just want to be sure it's notold.