Iif ( [Current Year's Actuals] <> 0 and NOT IsEmpty([Current Year's Actuals]),
([Current Year's Actuals] - [Current Year's Budget]) / [Current Year's Actuals], Null) 

Iif( Max ({Descendants([Store].CurrentMember),[Store].CurrentMember},
Abs([Category].CurrentMember)) >= .5, RGB(255,0,0), //red
Iif( Max ({Descendants([Store].CurrentMember),[Store].CurrentMember},
Abs([Category].CurrentMember)) >= .25,RGB(255,255,0),  // yellow
Iif( Max ({Descendants([Store].CurrentMember),[Store].CurrentMember},
Abs([Category].CurrentMember)) > 0, RGB(0,255,0), //green
RGB(255,255,255))))  //white