Is it a condition for a woman's prayer attire that it not be decorated, shiny, or of striking colors, or are these conditions specific to the hijab and not a condition for the validity of the prayer?

The conditions for a woman's prayer attire are that it must cover her entire body, except for the face and hands. It does not matter if it is ornate or colored. Scholars have recommended praying in one's best clothes, based on the verse: "O Children of Adam, take your adornment at every place of prostration [or prayer]." This address applies to both men and women, so a woman is commanded to cover herself during prayer, even if she prays alone.