Need help with the structure of a sentence

[Niddelaj]

I have a pretty simple sentence, that I just can't seem to agree with my friends about.
I'm not a native english speaker so mistakes can be present. The first sentence is what I've written and the second is what my friends argue is correct.

The colour should be blue, where otherwise not specified.

or

The colour should be blue, where not otherwise specified.

[Alan]

I'm afraid that your friends are right!
A more natural expression, however, is 'unless otherwise specified'.