"Chain from [quality]--[text]" means that this spell has the specified ability (usually a spell ability, but it might not be) from when you start to cast it until it leaves the stack, if all of the following conditions are met:
- Either you had cast a spell with the specified quality, or played a land with the specified quality, or a spell with the specified quality that you had cast has resolved.
- You did not do anything else with your priority (including passing) since the most recent such event occurred, other than cast the spell with this chain ability, and optionally mana abilities.
- The event occurred during the same step of the same turn (e.g. you cannot chain from the resolution of a spell that ends the turn).
Once it gains the ability, it does not lose it until it leaves the stack, so changing the conditions so that they are violated will not remove it (nor will changing its text, e.g. if the quality is "red", then Sleight of Mind cannot change whether or not the chain condition is met.
