Madeleine Swann (played by Léa Seydoux) can be seen holding a brown Chloé Marcie Small Saddle Bag in the Bond Women video blog and promotional images for movie SPECTRE.
The color of the crossbody style bag is probably "Tan" (although hard to see exactly), a soft, supple lambskin with matte goldtone hardware. The ridged front has a hidden pocket underneath flap. The fold-over flap has an o-ring and leather strap closure. Buckle adjustable shoulder strap. Fabric lined with single patch pocket.
The bag measures approximately 7'' (19cm) at widest x 6'' (16cm) tall at center x 3½'' (9cm) deep; weighs 1 lb (450gram).
Note that there are different sizes available for the Marcie Saddle Bag, it looks like Madeleine Swann is using the Small version.
Retail price of the bag is around $775. A tan leather small Chloe bag is now on sale at Jomashop for $445 or you can find the Chloe Marcie at Liberty London (£435).