I also doubt that anyone would go for Colston + Jackson for LT2 + Marshall.
Marshall's a viable mid-level WR1 the rest of the way (at least), but LT2 is, at best, an RB2. Although if you know of any owners in your league who have a serious man-crush on Tomlinson, defintely try to sell high.
My guess would be that you'll probably have to settle on packaging LT2 + Marshall for a solid RB1 and something like a WR3, or a buy-low WR2/TE, depending on if your league's PPR or not. You could try to target Ray Rice, whose owner may not yet fully appreciate him. Or maybe try to grab Thomas Jones or DeAngelo Williams somehow.
If you're dead-set on Jackson, you're going to need to downgrade significantly from Colston, given that Jackson's a major upgrade over LT2, and Colston is still an upgrade over Marshall.
Given Slaton's benching on Sunday, you could also try to go LT2 for Slaton, if his owner is completely dismayed. Then again, this assumes you see an upside to Slaton. Dunno if anyone would go for that at this point, though.
(0.5 PPR, 12-team league)
QB: Vick, RG3
RB: McFadden, Matthews, K. Smith, R. Williams, M. Goodson
WR: Nicks, S. Smith, Britt, LaFell
TE: Hernandez, Pitta
DEF: Spot start (Cin in wk4)