Multiple icons or icon and color (font/background) for meta-info?

I have a webapplication where users are shown work-related warnings in a table. Each row is one warning. Hovering over a cell shows full field name. Cells contain text or numbers, only importance is indicated with an icon. If a certain number reaches a threshold the icon appears. The users are familiar with this.

I want to add a similar field, indicating a certain duration has passed some threshold. Is it better to add an another icon or to use a different font color or background color for that row?

Users are familiar with the icon-design. Hovering over the icon specifies the field name. On the downside, i have to reserve two columns for icons and a checkerboard of empty spaces alternating with icons clutters the otherwise clean design.

Instead i could use a different font color or a different background color as an indicator. If i manage to avoid picking colors that make the interface look like a clownsuit, i think this would look better. The main disadvantage is that there is no text to indicate the meaning of the coloring.

Edit: a third option might be to do something to one of the other fields. Like add markup and explanatory text to the hover in addition to the field name.