Peachwool, Nida and Bon Bon are some of the suggested materials to use for a ladies ihraam.
Here are some pros and cons of using either colour.

Black

Pros

• No need to wear double layer as it is not see through
• Dust etc wont be easily visible

Cons 

• might attract more heat

White

Pros

• Looks beautiful seeing a see of white
• Reminds one about wearing a white kafan after passing away

Cons

• Dirt etc can be easily visible (note for ladies who get their menses to avoid wearing white)
• A double layer of clothing may need to be worn as material might be see through

Its a personal preference which colour to wear.

In the end, we make duaa to Allah that our hearts become white and pure after performing Hajj – Aameen