I have been trying to solve this problem recently. I have tried adding a space and "A" or "D" for ascending or descending after the column name. I tried putting " *" after the name to indicate the column is sortable.

My latest solution is " ^" (carot) and " v" (lower case V), with " -" (minus) after the name to indicate the column is sortable.

I think colors would be too hard to remember, since there are no logical colors for ascending or descending.

>Is it possible to put two different fonts in a header? For example, "Header" with a uparrow or dnarrow to show ascending or descending order of the column.