When fresh cut, Cherry has a white sapwood that turns almost as dark as
the heartwood as air & light get to it, so probably it will mellow.
The heart & knots are darker & will stay that way, but the difference
isn't nearly as severe. Usually it turns during the drying process,
but it is very light sensitive. If you can wait a week, I'd put the
board in a sunny place & see if it doesn't change some more. - Jim