I have a web site which I specified background-color: #005181; using CSS.
If I open that page in browser and then check what is the background color using a color picker extension, it is #065181.
If I use GIMP and pick color from screen, it is #065082 picked from Chrome and #064e84 picked from Firefox.
I've checked in devtools and the CSS color being applied is #005181, but it is being rendered differently on the page.
OS: Fedora Linux 39 (Workstation Edition) GNOME 45.4 (X11)