The Dark seasons contain a True Autumn undertone. For this reason, they are deeper, but a bit more muted.
The Bright seasons contain a True Spring undertone. For this reason, they are lighter and brighter.
Let's go back to the foundation. True Winter:
We have the three primary colors: Red, yellow and blue in their purest form.
Pure black and white are also present.
True Winter is one of the two Cool seasons, the difference between it and True Summer is, True Winter is cold like hard frozen ice. True Summer is cool like flowing water. But, I digress......the point being made here is True Winter has, as its base the coldest colors you can find of the 12 palettes.
Quite a bit more warmth is added with Dark Winter. In True Winter, there are no fiery embers. With Dark Winter, don't be mistaken... cold, brisk Winter air with snow and ice exists. However, the bonfire has dimmed down to simmering embers.
To use photo analogies, True Winter is crisp and contrasting:
Dark Winter is rustic:
If you are deciding between both of these seasons, what do you need to look for?
1) Pure black and stark white prints look right at home on a True Winter. Dark Winters can't get away with that to the same degree. Their black and white needs to be softened down, just a tiny bit for balance.
2) A True Winter needs polished shine. A Dark Winter looks better with some texture. If you are a Dark Winter, choose the alligator skin black shoes rather than the sleek patent leather your True Winter sister would wear.
3) True Winters can wear a very cool toned lipstick that has a pure purple base, or a primary red. Dark Winters do much better in wine and cranberry colors.
4) Color saturation. A True Winter palette is very high in chroma, though not as high as the Bright Seasons. If True Winter is absolutely cool and at 85-90%, Dark Winter is at 75%.
5) True Winters wear polished silver, white gold and platinum very well. Dark Winters can wear silver and gold metals, provided there is texture added, like a hammered finish or something with an aged patina.
These are the most obvious differences I can think of. Dark Winter and True Winter are the closest sisters, as far as the seasonal spectrum goes. It all boils down to what you need...contrast and smooth shine, or depth and texture.