Could the darkness have almost completly vanished and it's a normal red heart again with maybe just a few hints of darkness in it or could a fair amount of darkness be still there and her goodness comes from her soul since she was still plenty good even without it since she was able to use light magic with true love's kiss without it?
But it has to be lighter then it was before. Just a little lighter? I mean, she's been doing good for about three years now. Surely, at least some of the darkness has vanished. I mean, she rescued Marian twice (even though she was Zelena but still), she revived a horse in the Underworld, she saved Roland from a flying monkey, she allowed Emma to take Henry to the outside world when Pan's curse engulfed the town and gave them false but good memories in replacement of their real memories having to be wiped, and she helped her father go to a better place in the afterlife. Surely, that must have gained her some darkness vanishing points. I think some of the darkness might always be there but I believe she can be capable of letting a fair amount to vanish.
Regina has done good for a few months....at most. Apparently it has only been 2-3 years sense Emma's birthday. I'll say it's "less dark" but nothing too noticeable, but it's not like she's pulling out her heart.
I'm thinking... these deeds do little amends to her almost darkened hearts, then maybe... a major sacrifice, disintegration, reassembly? Taking one for the town, deceased, offered choice into heaven or back on the ground, chose ground and rematerialized, maybe?
Actually, the question makes me wonder why ANYONE has a red heart with no darkness. We saw Snow's with one little spot, but that one should really be more than just one spot. David's (before it was crushed) was clean and there is no way, given the number of lives that he took as a knight and prince, that it should be clean. Emma's (once we finally got to see it) was pristine, and sorry folks, but it should be speckled. Henry's was clean in Neverland. And while it may be the heart of the truest believer, and Henry has never killed anyone, it should be speckled (Running away from home and town, coupled with some of the stunts he pulled).
Point being, everyone's hearts should be dark to some degree or another. and I don't think that any amount good deeds will clean up the damage done. It would take an outside force to come in and clean Regina's heart of the darkness. She can (and does) take actions now that prevent her heart from darkening too much more, but it doesn't change the damage that her past has done. And it also does not prevent her from being redeemed.