Change colour of bar in a bar chart depending on previous bar values

[david_pearson]

Hi all, i have 2 bar charts. i want to colour each bar depending on the previous bar vol/value. For example. if bar 2 (2M OD) is greater than the value/vol  of "1M OD" then i want it to be coloured red. If lower than the previous bar then green. Note that the dimension may not always be there as per image 2. The dimension im using is called "AGEING" and my expression is below...as you can see variable buttons are being used too. Presumably this needs to be a colour by expression??

if($(vButtons)=1,
num(count(distinct{<COLL_STATUS={'Overdue'},[REPORT_DATE.autoCalendar.YearMonth] = {"$(=Date(AddMonths(Max(TOTAL [REPORT_DATE.autoCalendar.YearMonth] ), 0), 'YYYY-MMM'))"}>}COLL_POL_NO),'#,##0', '.',','),
if($(vButtons)=2,
num(count({<COLL_STATUS={'Overdue'},[REPORT_DATE.autoCalendar.YearMonth] = {"$(=Date(AddMonths(Max(TOTAL [REPORT_DATE.autoCalendar.YearMonth] ), 0), 'YYYY-MMM'))"}>}COLL_AGENCY_REF),'#,##0', '.',','),
if($(vButtons)=3,
NUM( sum({<COLL_STATUS={'Overdue'},[REPORT_DATE.autoCalendar.YearMonth] = {"$(=Date(AddMonths(Max(TOTAL [REPORT_DATE.autoCalendar.YearMonth] ), 0), 'YYYY-MMM'))"}>}GBP_NET),'£ #,##0', '.',','))))