A solar screen is a woven cloth with a published openness factor — 1%, 3%, 5%, 10% — and that percentage is the share of the weave that is open. At 10% you keep the view almost intact and let a good deal of heat and glare through with it. At 1% the cloth reads as nearly solid, cuts the glare down to almost nothing, and still is not a blackout: light comes through the yarn itself, and a screen at any openness will show a bright rectangle where the window is.
The second choice is the colour of the yarn, and it works against itself on purpose. A dark screen absorbs rather than reflects, so you see out of it far better and the room stays a little warmer; a light screen bounces heat back at the glass and washes the view out. West-facing rooms with a screen you want to look through usually end up dark and tight — a 3% charcoal is the shade this county buys most — and a north window that only ever needed the glare knocked off is fine at 10%.