Fuck no, man. I'm just gathering evidence to spring upon you like some monstrous beast. You'll see... ::cackles madly::

Yep. all you have to do is check out some of the gallery pics in MP... there's a Smaus face study that's pretty detailed, and it clearly shows Samus as a blonde. You can also beat the game with a high enough percentage complete and she takes off her helmet in the closing cinema. She's blonde there too.

In the original Metroid, Samus was either a very light brown, or a slightly dark blonde.

In Metroid II: The return of Samus, she was in 2 colors (black and green), so the question doesn't really apply to her there.

In Super Metroid, Samus had brown hair (and a cute little haircut too).

Which brings us to Metroid Prime (see above).

And then there's Metroid Fusion, where (again) Samus is, in fact, blonde.

For reference, as far as I know the Metroid timeline, MF takes place at least after super Metroid, though I don't know if MF happens before or after MP. Check out the pics, they speak for themselves: Metroid Fusion ending screens.