The torsion form can be defined as the exterior covariant derivative of a solder form, $\Theta=d_\omega\theta$. This derivative is always in the fundamental representation of the algebra $\mathfrak g$ or it can be in any representation?
Namely $d_\omega\circ=(d + \omega\wedge_\rho)\circ$ with $\rho$ the fundamental representation of the algebra.