Does Isochron Scepter let you cast the imprinted card even if you don't have the colored mana for it?

Isochron Scepter's activated ability reads: you may copy the imprinted instant card and cast the copy without paying its mana cost. The phrase 'without paying its mana cost' is the key — it bypasses the normal payment requirement entirely, including any colored mana symbols (CR 601.2b, CR 702.97a).

Casting a spell 'without paying its mana cost' means you simply don't pay the mana cost at all. You are not substituting another payment; you are skipping that part of casting entirely. This is explicitly covered in CR 601.2b, which states that if an effect allows you to cast a spell without paying its mana cost, you do so without paying it.

There is one important nuance: if the copy has an additional cost (like a kicker cost) or an alternative cost, you may still choose to pay those. But the base mana cost — including all colored pips — is simply not paid.

Concrete example: You imprint Lightning Helix (cost {R}{W}) on Isochron Scepter. Even if you have no red or white mana available, you can activate the Scepter for {2}, make a copy of Lightning Helix, and cast that copy for free, dealing 3 damage and gaining 3 life.

Citations: CR 601.2b covers casting spells and paying costs; CR 702.97a covers imprint; the 'without paying its mana cost' rule is detailed in CR 601.2b and the general rules on alternative costs in CR 118.9.