Should the themed function rely on global SCSS variables for validation?

[Carnageous]

Currently, the themed function uses global SCSS variables to

1. Check if the given value name exists in the themes
2. Add the pre-defined prefix to get the right CSS variables.

This is nice, but requires the global SCSS variables to be defined in the current scope, meaning that each SCSS file needs to re-define themes by calling the themes mixin. This can easily be done with a global.scss file, but it adds complexity.

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Question 1: Should this be the default behavior?

Question 2: Is the $verify argument of the themed function elegant enough to bypass this requirement, or should we rather add a second themed-like function that doesn't do validation?

Question 3: Should we remove the option to add custom prefixes, as this is also using a global SCSS variable?

Question 4: An alternative to this would be to return the themed function from a themes function (like a factory pattern). Would this be a nice alternative?