With reds, I do the tilt too, but I also put the glass down, and look straight down to see if I can make out the stem.
When I’m looking at whites, I tilt the glass at 45 degrees over the paper, and look at the rim of the wine for hints. For example, Sauvignon Blanc tends to be very pale, almost watery, and sometimes has a bit of green in it. With reds, I do the tilt too, but I also put the glass down, and look straight down to see if I can make out the stem. If I can’t see the stem, I call a wine opaque.