CAD tip # 7665:

The most convenient is the EATTEDIT command - this command is also invoked when you simply double-click on a block reference. Go to the Properties tab (the 3rd one) a select the new color for the given attribute in the Color list:

In the older versions of AutoCAD and AutoCAD LT you can also use the commandline version of the attribute editor: -ATTEDIT. Confirm the default Enter on the first 4 prompts, then select the attribute and use the Color option to set it to the new color. You can also use the menu macro:

_-ATTEDIT;_Y;;;;\;_Col;\;