Sheer fabrics have the finest weave and allow sunlight to stream through during the day while maintaining daytime privacy. Depending on the tightness of the weave, outside views can still be preserved while the blind is down.
Sheer fabrics provide good UV and heat protection.
If heat protection is a top priority for you, choose a fabric in a lighter shade to ensure maximum heat reflection.
If clarity of the view to the outside is important, choose a dark colour.