Ideas for versatile clothes in northern India

Since you specifically mentioned Leh/Ladakh I would like to mention a specific garment which any traveler should buy or carry there. It's a Pashmina Shawl/Wrap! They are relatively quite light and surprisingly very warm. They are relatively exotic to Ladakh as well. It would not only be useful but would make a great souvenir. They are a delicacy in other parts of India as well but should be relatively cheaper in Ladakh.

The pashmina shawl should take care of you at any point of time during the cold. Accuweather and Wikipedia tell me that the temperature of Leh should not go below 0°C for the duration of your stay.

Including this, for other periods of time a light windcheater which can be easily folded would be suitable.

This should take care of any temperatures >0°C quite easily. If you plan to go high up in the mountains, you should consider a heavier wool jacket.

Except this, you can carry regular clothes just like you would normally for a temperature of 25-30°C.

Instead of worrying about versatile clothes, I would simply buy any necessary warmer clothing when I get there. Prices are cheap: I paid something like Rs 600 for a "North Face" parka in Dharamsala, and while it was almost certainly a fake, it did its job in keeping me warm. When it's time to head back to warmer climes, instead of carrying it with you, you can just sell it or pass it on to another traveler.