Alexandra's evening dress, year circa 1898

Sources:

https://www.hermitagemuseum.org/wps/portal/hermitage/digital-collection/12.%20costumes%2C%20uniform%2C%20accessories/1246667/!ut/p/z1/jY_LDoIwEEV_BfZoC0JZNzURUawhPmo3piGATaQlFFz49VbjykR0dpOcO-cO4IABrsRN1qKXWomr3U8cnSnGyJ8RmFISzSGm-TbKyWYB_RAcXwD8MhgC_k9-BODj59NfAvtB0GUkqwFvRX-ZSFVpwPxg6hTa9ENTGs8ZlKx013iOKIrSGN3J0jyZECEU24r8Q7JcxVayixJKDyQg4RsYqdk2e3ZfJ1Bi130ApB2Ogg!!/dz/d5/L2dBISEvZ0FBIS9nQSEh/?lng=en

https://vk.com/album-4269989_180377989

https://vk.com/album-3643162_72617488

(photo courtesy of The State Hermitage Museum)

(photos courtesy of The House of Romanov (Dom Romanovih) on VK)

In the 1898 formals she wore the feather boa likely seen in this photo:

(photo courtesy of the Empress.Alexandra page on VK)

And in addition to other decorations she also wore the skirt from this dress:

The colour of the skirt would not have matched the colour of the rest of the other dress, but it didn't matter since the photos were sepia.

(photos courtesy of TatianaZ on Flickr)