I bought gray/white stripe.  I would say they do not "darken" a room, but they do block some light because they are not sheer.  The fabric looks like it may hold up to the sun, but is not quite as dense as Sunbrella fabric.  They are lighter weight than canvas, but have a similar feel.  I am happy with them.  I putting them on curtain rods  outside to block some sun rays before they get through my windows.  I am trying this instead of exterior sun shades.