The color seems to be linked to the foreground in themes. I assume it\'s using less alpha. Is there a way to control this?
You may want to try installing PersistentRegexHighlight from Package Control and then use a blank-character regex like [\x20 ] to add a specific color or color scope.
[\x20 ]
You'd want to combine this with drawWhiteSpace: "all", in Sublime user prefs.
drawWhiteSpace: "all",