Insert the green circle into a document. Change the wrap to InLine. Select and press ALT+F3 save in the normal template as an autotext entry called CircleGreen. Change the colour to red and save that as an autotext entry called CircleRed, repeat for any other colours you require. You can then use the following macro to replace the cell contents that contain the words red, green etc with the appropriate autotext entries, using the following macro.
The macro looks in all cells, but you can restrict to a column if you wish.
Option Explicit
Sub AddCircles()
Dim oTable As Table
Dim oCell As Cell
Dim oRng As Range
For Each oTable In ActiveDocument.Tables
For Each oCell In oTable.Range.Cells
Set oRng = oCell.Range
oRng.End = oRng.End - 1
If InStr(1, LCase(oRng.Text), "green") > 0 Then
oRng.Delete
NormalTemplate.BuildingBlockEntries("CircleGreen").Insert oRng
ElseIf InStr(1, LCase(oRng.Text), "red") > 0 Then
oRng.Delete
NormalTemplate.BuildingBlockEntries("CircleRed").Insert oRng
ElseIf InStr(1, LCase(oRng.Text), "black") > 0 Then
oRng.Delete
NormalTemplate.BuildingBlockEntries("CircleBlack").Insert oRng
End If
Next oCell
Next oTable
lbl_Exit:
Exit Sub
End Sub