In choice fields, each choice (item) can be set to a color, and the text can optionally be set to that color. In other field types, you can set the color of the field within its font settings. If you want to set an indication conditionally, probably the best way would be to set a choice field to a value that has the color you want.
Alternatively, you could define a red date field and a white date field and have the visibility of each of them be dependent upon a choice field you've set, so the one colored the way you want will be displayed. Making it conditional would entail a trigger script.
Try defining a radio buttons field Recheck with a red item called DUE and an uncolored item called Pending. Define an Opening the library trigger that goes through all entries, setting the Recheck fields as appropriate...
var daysCheckAgain = 5;
var entries = lib().entries();
for (ex in entries) {
var ent = entries[ex];
var dateCheckAgain = ent.field("dateLastChecked").getTime() + (daysCheckAgain*1000*3600*24);
if (Date.now() > dateCheckAgain)
ent.set("Recheck", "DUE");
else
ent.set("Recheck", "Pending");
}
I'm not a big fan of such looping through things; it makes things run slowly and doesn't deliver the big bang I would want for doing all that.
You could maybe avoid the looping by just doing it entry-by-entry by doing a non-looping version of that trigger in an Opening the entry edit card trigger instead.
If you decide to use date fields dependent upon the choice field, just make one of the date fields the "master", and the trigger can copy the value to the other date field to keep them in sync. I'm not a big fan of this technique, either.
I think the entry color would work fine for me.