If I am adding a chord to a chord progression and its from a parallel or dominate 5th substitution what scales am modes go with that substitution? If I am substituting a dominate 5th chord for a the 2nd chord in the major in the progression how do I choose the right scale or mode to highlight the color of the substituted chord?
Guessing you're talking about tritone substitutions. In that case I guess you could use either the scale built off your 7th chord or the scale built off the natural ii chord. You could also use a diminished scale/arpeggios or dominant-diminished build from the same 7th chord as well.
Or just, ya know, whatever you think sounds good.