"I have a white scarf."
Translation:عِنْدي وِشاح أَبْيَض.
There is a difference: أَبْيَض /abyaD/ is masculine and بَيْضاء /bayDa/ is feminine.
Here, the adjective white describes the noun scarf. On the other hand, one should know that scarf = وِشاح is masculine in Arabic. Therfore, you have to use the word أَبْيَض