Whenever I try to represent orchestral colour I just hear what I'm playing as say a cello having the melody (like the opening of Liszt's Valle D'Obermann, ) and play with a legato connected sound, as if my fingers are the bowing of a cello.....I'd say the way you articulate certain passages can convey specific orchestral sounds as long as it is controlled.
I'm reading that and I'm not sure how much sense that makes...but here's another idea. Earlier today I was listneing to the Overture to William Tell, and reading a long with the Liszt piano transcription (it is EXACT). Maybe get a copy of the score and read along while listening to the orchestra play it. Try certain sections out...the slow opening is an alright sight read, and because you have just listened to it you know exactly which instruments are represented in the writing. There's a trickier part a little later on that's really impressive in its orchestral representation where the english horn is playing the melody with i think, some sort of bass instruments playing chords underneat, and a nice little flute passage on top of this. Practice maybe just a section of it. And work on imitating each as the instrument it represents.
Try to hear it in your head, and maybe it will come across in the playing? hope this helps/
your friend
Rob