It is not permitted that men wear ornamental rings. Rings, which are used for blessings, are not a problem. Therefore, the pilgrim should abstain from wearing ornamental rings, even if they are used for ornamental purposes or blessings.
Wearing ornaments is absolutely Haraam for a woman in the state of Ihram, but ornaments that she normally uses can be worn in the state of Ihram if she hides them.
Using henna is not permitted for men and women if it has ornamental purposes.
It is an obligatory precaution that a Muhrim (man or woman) abstain from wearing any other kinds of ornament. He/she should not wear ornamented Ihram clothing of sandals and abstain from any kind of makeup and decoration on the head, face or other parts of the body.
Coloring the hair has problem for a Muhrim if it is called decorating, even if he/she have not intended for decoration, and if it has no decorating purpose (like using henna for treatment) then there is no problem in doing that. Also coloring the hair and using henna before Ihram in the way that its effects remain until the time of Ihram has no problem, unless the pilgrim had intended for decoration for Ihram from the beginning.