Here is an example that can get you started. The code below assumes
you have a value in cell  A7 and a bar  or column chart  showing that
value. Put this code in the sheet by right-clicking in the sheet's
tab and choosing "view code".

Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Address = "$A$7" Then
Set x = ActiveSheet.ChartObjects("Chart 1") _
.Chart.SeriesCollection(1).Interior
If Target.Value < 0.25 Then
x.ColorIndex = 46 'Orange
ElseIf Target.Value <= 0.5 Then
x.ColorIndex = 3 'Red
Else
x.ColorIndex = 4 'green
End If
End If
End Sub

Only trouble now is how do I expand the code to say work with the
next cell  as in A8 and A9. I have copied the existing code and
changed the cell ref but now it changes all the columns to the same
colours based on the value of what is in cell A7

Here is a modification that takes the data from the chart  rather
than the sheet, so it doesn't mater where the data is. It also goes
through all charts on the sheet. I tested it for the basic bar  and
column charts only. Brad

Private Sub Worksheet_Change(ByVal Target As Range)
For Each MyChart In ActiveSheet.ChartObjects
MyVals = MyChart.Chart.SeriesCollection(1).Values
Set MyPoints = MyChart.Chart.SeriesCollection(1).Points
i = 1
For Each p In MyPoints
v = MyVals(i)
p.Interior.ColorIndex = ColorScheme(v)
i = i + 1
Next
Next
End Sub
Function ColorScheme(v)
If v < 0.25 Then
ColorScheme = 46 'Orange
ElseIf v <= 0.5 Then
ColorScheme = 3 'Red
Else
ColorScheme = 4 'green
End If
End Function