I've accidentally set ColorSync to websafe colors.
I'm not even sure how you managed to do that. That profile is not a choice under Displays. Nor is it a choice in ColorSync Utility if you try to create your own profile under Filters.
If Vilas_S' method doesn't help (there is no custom ColorSync profile to remove), then try this.
System Settings > Displays
If you can't read the left column entries, then just count the spaces from the top. The first is between your user name and Wi-Fi. Then go three more spaces down, where Displays will be the second choice in the next group.

Once selected, you can see here where the Color Profile drop down menu is. Click that and choose quite literally anything, even though you may not be able to read the entries, so ColorSync is not using Web Safe Colors as the monitor profile. The top one as seen below, will be the generic, default monitor profile.
