Hmmmm, as much as I love variegated and colored leaves, the one color I usually don't care for is yellow, it always looks like it's dying to my eye.

Yellow and chartreuse-leaved plants are excellent (along with silver/gray) for lightening up and providing contrast in color schemes based on purple and black foliage.

I have a spirea ('Lemon Princess') that handles this job nicely. And I have high hopes for a chartreuse-leaved smokebush.

Nigella - I have to admit I felt the same, but this year I planted some Lysimachia Nummularia 'Goldi' as a groundcover in my full shade garden, just for something different than mulch, thinking that if I didn't like it the hostas would soon overshadow it anyway. Hating to own up to it but it seriously makes everything around it POP in a way the black mulch never managed to; everything just looks MORE the color it is. Kind of like adding spice to a dish that was pretty good before without it.