not sure how much control you guys have over this, but then again, AFAIK the Spectrum texture option was added in i25, so...
I was working on a concept character, idea was a being of living plasma partially escaping his containment suit, was able to get pretty close with Robotic Arm 3 using an armored chest detail covering most of the torso, leaving the left arm exposed with the Spectrum option on the underlying Torso, but then I discovered that Spectrum had been left out of the options for the Glove.
It is an option on the Robotic Arm 2 Torso, so this seems to be more of an oversight than a deliberate omission.
Ultimately, it'd be cool to get a 'normal' arm option for Robotic Arm 3 (one that could be detailed separately from the Torso and Left Arm), or even better an Energy Arm- but those are suggestions for another day...