Short answer: no.
Long answer: pillar's restriction means that the mana can only be used to pay the casting cost of a multicolored spell (such as replicate). Paying for the Isochron scepter ability, although it will ultimately be used to cast a multicolored spell, is not paying the mana cost of a multicolored spell.
But "replicate" is an activated ability, such as the copy from scepter. The main difference between both abilities is the source, which is an artifact (colorless) or an instant (multicolor), however, the source should not matter but the text of the effect. If you activate isochron's ability, it casts a copy of a multicolored spell (the imprinted card), if you activate replicate, it casts a copy of a multicolored spell. (Bare in mind that
Isochron scepter text from mirrodin says "You may copy the imprinted instant card and
play the copy without paying its mana cost.". And paruns text "Add one mana of any color to your mana pool. Spend this mana only to
play a multicolored spell." It should be legal, because the source should not matter. For instance, devoid cards cannot be paid with pillar, not due to the source (multicolored mana) but to the spell (colorless).