QSOs can be color coded in the log tables for your convenience. RUMlog itself uses magenta text color to indicate for DXCC invalid QSOs. The user can select the background color. You can choice the color during logging from the provided popup in the logging mask, or you can change it later. Select one or more QSOs in the table and go to: Menu–>QSO–>Color code
This works in the Search windows as well, so you can mark the found QSOs on the fly.
In the quick search section, you will find the Color code popup on the right hand side. It may be is required to widen your window.
During a contest-log or ADIF import, you can chose directly a color for the QSOs to import.
The color code will be exported in an ADIF file and can be reimported. This is not an ADIF conform function, so it works in RUMlog only.