the source
The colour scheme of the apprentice's outfits can be determined with certainty from the model renders. Screen grabs are useful for support, but will be influenced by ambient lighting. In game models are also less favourable as 501st reference when the full detail models are available.
I would consider the models created for
The Force Unleashed to be the primary source above all others.
There's one last notion I'd like to offer in regards to possible standards for the 501st--this comes form my experience as the 501st Legion Membership Officer;
Consider Anakin Skywalker;
When the first production shots of his Episode III appearance were leaked, folk began making a brown costume with black tabbards, black boots, and belt. Even the first toys made in his likeness followed this scheme
A little after the dust settled it was found that in fact, no black exists in his costume. In interviews the designer of Anakin's costume expressed how the total absence of black in Anakin Skywalker's costume for Episode III was intentional.
In the year and a half I approved Sith Lords for membership in the 501st, I estimate deferring as much as two dozen applicants whose costumes were based on screen perception. (Many made the suggested adjustments and were later approved.)
There will be a little bit more of a process with Force Unleashed characters.
I urge readers of this forum interested in making the Secret Apprentice and seeing it in the 501st, to join the forum designed for this purpose;
The 501st's Expanded Universe Detachment; The Flagship Eclipse.
Hoping to see you there,
Thomas