Today marks the start of what liturgists are wont to call Holy Hell Week. Lots and lots of celebrations, whole hosts of special ceremonies and traditions to include, and, by the time we get to the Paschal Triduum (Holy Thursday, Good Friday, Holy Saturday), there are three complete "set changes" to do in as many days. The proper color for Lent is purple, but the Mass of the Lord's Supper on Thursday is a Eucharistic feast, so that means white vestments and paraments. That's also the day on which we commemorate the Mandatum, the washing of the disciples' feet--so the liturgist has to round up a dozen or so people willing to have their feet washed, and make preparations for that. After Mass, the Blessed Sacrament is exposed, usually until midnight, but in some cases all night long, for people to pray in commemoration of Jesus' admonition to the disciples in the Garden of Gethsemane ("Could you not remain awake for even an hour?" Mark 14:37).
Good Friday, being a feast of the Passion, means red vestments and paraments. It's also (a) not a Mass, (b) a day when it's traditional to remove or cover all images in the church, and (c) the day on which Catholics venerate the cross in a special way, which of course requires a major rearrangement of the worship space. The Passion narrative is read out again, which almost always means multiple lectors and some crowd participation. After the service is over, it's tradition that the altar is stripped bare and the tabernacle left empty and open (though the Sacrament is reserved in a secure place elsewhere for the sick and for Viaticum).