Rienaldo,
According to Microsoft's documentation, there is a color setting for this:
COLOR_GRAYTEXT Disabled (gray) text in buttons. This color is set to 0 if the current display driver does not support a solid gray color.
See here:
http://msdn.microsoft.com/en-us/library ... 41(v=vs.85).aspx
I hope this helps.
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I note that you are using a button labeled "Exit." Assuming this is on some type of a data entry screen, this is not the Windows standard--"exit" is reserved only for exiting a program. When you use it elsewhere it is confusing to the user.
If the screen is modal, standard terms are "OK" and "Cancel." I am assuming your example is a non-modal window, and in this case the standard terms would be "Save" and "Close."
Just FYI.
Regards,
James