How to match colors across dual monitors that look different

Open the tool in a window on each monitor. Create a session in the first window, then join from the second with the 4-character code or the share link. Put each window in fullscreen on its own monitor, and leave the page on its light gray. Open each monitor's on-screen menu, set the brightness to the same level, and pick the same picture or color mode. Let the screens run for a few minutes before you look for differences.

Read the gray first. Tint and brightness differences show clearly on light neutral fields, so a single gray tells you a lot. Look for a color shift, where one screen is warmer, pinker, greener or cooler than the other. Then look for a brightness gap, where a gray is dim on one monitor and clear on the other. Once the gray matches, type a few saturated colors into the HEX field, such as #FF0000, #00FF00 and #0000FF, and write down which ones show a gap. A gap on one color and not another tells you which colors to watch in your own work.

This check judges the gap by eye, and nothing in the tool adjusts either screen. It sends the same color values to both, and it can't read what either one produces. A match may be partial, and the tool can't tell you how close is close enough. It also has no way to say which monitor is correct, so that decision stays with you.