The color difference between first and second line is not enough. You should never use only color to transmit information because lot of people are one kind of color blind Wikipedia color blind.
Lot of design choice on color apply to bad reading condition think mobile, sunny area...
It's better to have extra text, really simple icon, even a star on the line, or something at least color blind proof like strong text.
- You could merge Value and Custom columns. The important information is Default or Customized. So you could have only one combobox with Rubber Mallet (default), FiberGlass(option), Wood(option), Paper(option), R&D Polymer #5(User defined)
- Another option if to make one column with information Default, Option, User specified. And the other column always displayed the name, and make it editable only for customized by user.
- Column Type one of the 3 value (Default, Option, User specified) or 2 option (Default,Custom)
- Column Value one of (Rubber Mallet,FiberGlass,Wood,Paper,R&D Polymer #5...) This column should be editable only if user defined/custom is set.
Filling vs reading
Maybe you should provide an interface dedicated to enter information, and a really reduced one only to display the choices. If user don't need the information all the times remove it, and provide a way for exceptional case to access the edition form.
Ask yourself questions on everything
Is it absolutely the best option to edit inside grid or a popup menu with more space to provide options like the more commons options or the 5 last customized...