Just looking through TF Yuki's tweets, and I think this is the pic that was used for Blast Off's colouration:
http://i.imgur.com/SHW52qt.jpg
The brown is a lot more noticeable in this pic than the others. Although the only problem is, the brown on the toy is too light!
That said, the brown in the 'toon pic does look similar to the brown in the combined mode in this pic (although Vortex looks too dark here):
http://i.imgur.com/r4sG3DE.png
And the brown on the chest looks similar as well to the 'toon here:
http://i.imgur.com/XlOddpZ.jpg
We definitely need some in-hand shots!