Suppose Poe w/ Black One reveals a 4K. Leia spends a force to make it white. He executes the maneuver then uses Black One to SLAM another 4K. Is the second 4K white as well?

Heck knows the card is poorly written and it's unclear.

No - it's only on the dial flip and specifies 'that maneuver'

General consensus is, as @The Penguin UK stated, only during the reveal and execution of the maneuver itself. The poor language on the card, however, leaves room for interpretation, as @thespaceinvader has pointed out. There have been arguments that her ability remains in effect for the entire round. Others claim (with no real evidence to back it up) that her changes last for the entire game , or even in perpetuity, lasting forever (cue Resistance Leia training montages, to make your entire team's dials blue forever)... but those positions are very hard to defend, given the design tendencies of the game as a whole.

33 minutes ago, emeraldbeacon said:

General consensus is, as @The Penguin UK stated, only during the reveal and execution of the maneuver itself. The poor language on the card, however, leaves room for interpretation, as @thespaceinvader has pointed out. There have been arguments that her ability remains in effect for the entire round. Others claim (with no real evidence to back it up) that her changes last for the entire game , or even in perpetuity, lasting forever (cue Resistance Leia training montages, to make your entire team's dials blue forever)... but those positions are very hard to defend, given the design tendencies of the game as a whole.

do not forget that some people (read: me) claim the card only works as written, limiting the timing that the effect lasts to whats printed on the card, as in "after a friendly ship reveals its dial", meaning the effect has no real use what so ever, since when you execute the maneuver the difficulty of the maneuver is no longer decreased.

if you want Cova Nell to work with Leia, i think it seems unreasonable to claim she works with SLAMing a k-turn with black one.

consensus on the timing of the decreased difficulty from leias ability is currently as @emeraldbeacon describes, something along the lines of "while you execute that maneuver".