I planted a new clump about two weeks ago. The leaves were green and the new growth is coming out crimson and staying that color, but the existing green leaves are still staying green. I can see the veins turning a little purple, but not much else. Will these existing leaves ever turn crimson with the additional sun exposure?
They might, they might not. All the newly arriving leaves should be burgundy, but remember that this colour fades down in late summer and turns to orange/red or yellow at leaf fall. When it leafs up again next year, hopefully all the foliage will be burgundy.