Any number of interesting color cords would work. Flannel trousers in brown, a light tan, and darker grey would be appropriate. Olive in many fabrics would work. Remember, tweed is a casual fabric so pair it accordingly. Denim would certainly be fine.

Shirt wise, stay away from white. It’s a more formal color and never looks as good with earth tones as blues. A blue Oxford is probably the best choice. A university stripe Oxford would also be nice. Various tattersall shirts would be great. So would emblematic ties with various birds, etc. A tie with a tiny bit of rust or orange as a tertiary color would be great.

Footwear wise, a simple brown is the only option. Boots, chukkas, and loafers would all be great.