Hi Alan
I don't know how easy that will be with formulas (or if even possible)
I would say use VBA.
something like:
Sub ColorCellCalc()
Dim wantedColumn as byte
Dim Sh_ as worksheet
Dim Tot_ as Double
Set Sh_ = Worksheets("Sheet1")
wantedColumn = 2 'which would be B, change it if you need a different one
For i = 1 to Sh_.cells(65536,wantedColumn).end(xlup).row
if Sh_.cells(i,wantedColumn).interior.colorindex <> xlnone then
Tot_ = Tot_ + Sh_.cells(i,wantedColumn)
end if
next i
Sh_.range("A1").value = Tot_
End Sub
hth
Carlo