Caution: This requires some amount of technical knowledge about how matrix/riot works.
For reference, the original grey color scheme in Riot had a primary color of #595959 and a secondary color of #ececec
- Open the developer tools by typing
/devtools
- Click the "Explore Account Data" button
- Click the "im.vector.web.settings" button (if you don't have this button, use the instructions below instead)