Depending on the light and growing conditions, this Ajuga can get very dark.
full to shade, deeper color in brighter light, foliage becomes crispy in hot dry site
prefers and grows faster in the moister areas, very slow in dry areas
Soil & Site
average to moist, not dry
spikes of blue flowers
scalloped leaves, to an almost black color.
3-6 inches tall, spread 10-12 feet or more, space 2-4 per square foot
very easy from division, rooting plantlets
#04-Herbaceous Perennial Plants (Allan Armitage), #68-Groundcovers for the Midwest (Voight, Hamilton, Giles)
Although I have never grown this particular Ajuga, I think it will also follow the Ajuga rules for great foliage color. It will need good soil, good light and the more the light the more water it will need especially during dry spells.