The Continuous Spectrum
Colour seasons don't live in separate boxes. They flow into each other like a colour wheel, each one sharing a little something with its neighbours. That's your whole spectrum of human colouring, one smooth gradient. It's also why some people feel stuck 'between' seasons, and why the odd colour works across more than one. Once you get how the flow works, you can grow your palette with confidence and spot which 'rules' are actually bendable.
Sister Seasons and Shared Characteristics
Sister seasons are neighbours that share one big thing in common. Light Spring and Light Summer are both all about lightness, they just differ in temperature. Soft Summer and Soft Autumn share that muted quality, Deep Autumn and Deep Winter share depth. Once you know your dominant trait, you can usually borrow from your sister season, especially colours that play to that shared strength.
The Light Sisters
Light Spring and Light Summer both have delicate, light colouring, and both look best in light to medium-light shades. Light Spring's are warmer and clearer, Light Summer's are cooler and softer, but they meet in the middle.
The Soft Sisters
Soft Summer and Soft Autumn share muted, gentle colouring, and both want complex, greyed shades. The difference is temperature. Soft Summer leans cool, Soft Autumn leans warm, but both can wear muted colours that sit right in the neutral zone.
The Deep Sisters
Deep Autumn and Deep Winter share rich, deep colouring, and both need that depth in their colours. Deep Autumn's palette runs warmer, Deep Winter's cooler, but both can pull off certain deep neutrals.
The Clear Sisters
Clear Spring and Clear Winter share bright, clear colouring with high contrast, and both want clean, saturated shades. Clear Spring's lean warm, Clear Winter's lean cool, but both can wear bright colours that stay fairly temperature-neutral.