When you removed the library you will have removed the reference to the technology used for the schematic and/or layout layers used. For the schematic the quick fix is to put the required reference back.
With ADS running and the problem workspace open use the Options > Technology > Technology Setup menu command in the Main window.
In the Reference Libraries tab at the top make sure the library you have open is set in the drop-down list at the top. Make sure that ads_schematic_layers is shown in the Referenced Libraries list. What you are seeing would be usual if this was not set. To replace it use the Add Referenced Libraries... button to locate this library and add it to the workspace library. Then when opening schematics the correct colors should be used.