purple is likely fine as long as its mold resistant its likely just a different color because of the manufacturer depending on your local area. i personally wouldnt cover the carpet with plastic or a tarp because moisture could condense between the plastic and the carpet causing the carpet to smell moldy i have my own grow room in a basement with concrete however if i had to have it on a main floor the cheapest flooring that would do would likely be a type of vinyl flooring. im sure tiles would be fine as well.
