Instead of requesting the typing of data in the characteristic value field, enable a subfunction that would let the user store some fixed values in a related table that could be displayed in a combo-box where an existing value could be selected or entered. This would reduce the number of errors when only a few values are used for a given characteristic that is repeated for many entries.
Characteristic name: Colour
Characteristic values: Blue, Red, Green, Black
The combo-box would contain the list of defined colours and the user could select one or type another one that is not in the list.
Steps to reproduce:
Read more at http://www.xtuple.org/mantis/view.php?id=8414