Crystal Reports how to select colors on detail line

Message

   Hello,

I have a 'DaysBehind' Field ..

If DaysBehind >= 4 
then
yellow
else
if DaysBehind >=8
then 
red
else 
default color;

I tried going to the detail line > color tab > and adding in a formula :

If ({DaysBehind}>=4) Then Color CrYellow 
Else
If ({DaysBehind}>=8) Then Color CrRed Else  

DefaultAttribute;

but it is throwing up an error 'the remaining text doesn't appear to be part of the formula (after the first 'Then')..

any ideas ?

thanks
Jenn