mono/MonoGame — pull request #1924 by danzel (2013-08-10 22:53:11+00:00)
Title: PremultiplyAlpha should be set true by default

DefaultValueAttribute does not set the value, just hints it.
http://stackoverflow.com/questions/1980520/defaultvalue-attribute-is-not-working-with-my-auto-property

This change means when building texture content with mgcb it will be premultiplied by default, matching the XNA default.