I barely understand slang rules, but borrowing from others I came up with a rule that removes color from Done items, turns past due To-Do's orange and current and future To-Do's green, and current and future Appointments with an A: or O: magenta and with HRG: red, and removes color from past hearings and appointments.
 
++:!+-MN:          
iff(gfv('Done') > 0, "",          
iff(gfv("To-Do's") > 0, (iff(gfv("To-Do's") < TODAY, 0x0099FF, 0xFF0000)),          
iff(gfv("Appointments") > 0,  
     (iff(gfv("Appointments")>=TODAY&&(left(itt,2)=="A:"||left(itt,2)=="O:"),0xFF00FF
,
           (iff(gfv("Appointments")>=TODAY&&left(itt,2)=="HR",0xFF,
"")))),      
"")))        
:          
[To-Do's] or [Appointments] or [Done]
 
 
I cannot remember where the skeleton of the above came from, and I am sure it is not the most elegant way to do it, but for now, I am just glad I got it to work without bother my fellow eccolytes overmuch.  --Chris Holly