I have lots of blue tarps around my house. Unfortunately several are used to keep pigeons from pooping on gear in my barn (wife won't evict them ... argh!!!). Some are clearly thicker than others, though I haven't kept track of where I've purchased them from and they don't have labels on them to allow some kind of backtracking.

The different colors seem to relate to thickness - blue=thin, brown=thicker, silver=thickest ... or something like that.

I even bought a couple of the bright orange plastic tarps just in case I need them.

When I was a kid my dad bought a bright orange nylon tarp/fly, but I've never found an orange one on-line. When I bought my Tundra Tarp for camping I caved in to the mute color green.