I'm going to jump on this teaching moment.
A priest wears special clothes during the Mass, these are called vestments. Vestments are used to show that the priest is not acting by his own power, but in the person of Christ. I'll go over the basic vestments used for the Mass, and I'll try to keep it simple. I'll also explain their meaning using prayers that priests used to say when they put them on, but this has since been made optional.
First the priest puts on an alb, a long white robe. The alb is meant to cover all the priest's clothes (save maybe shoes), and it represents purity. It's often explained as being like the white garment of purity we all receive at Baptism.
After the priest puts on the stole. The priest will also wear this for other sacraments, like Reconciliation. The stole represents immortality, priestly authority, and priestly burden. You can think of it as a yoke placed around the priest's shoulders, and also a mark of where Christ carried his cross (on the neck and shoulders).
The chasuble is the final, outer garment of the priest. This also represents the yoke of Christ, but it also represents charity. This is why the chasuble is meant to be worn over the stole during Mass: a priest's charity should be more prevalent than his authority.
This is a very simple description, and there are many more vestments. If there's anything else I can do to help, let me know.
Now, for the colors:
*]White is used most often. It represents celebration, and eternal life.
*]Green is used when no other color is perscribed. It represents the steady growth of the Church.
*]Purple is a penitential color. It's used during Lent, since this is a time of penance. It is also the color of the stole the priest wears when he administers the Sacrament of Reconciliation, which is penetential in nature.
*]Red is representative of blood or fire. It's used on the feasts of martyrs, and on occasions like Good Friday, when Christ shed his blood. It's also used on Pentecost and other Masses of the Holy Spirit, to represent the Spirit's appearance in toungues of fire.
*]Rose can be used two days a year, each near the end of Lent and Advent. It's meant to show that these penetential times will soon give way to joy. That's why it's a mixture of the two colors.
*]Black is optional for funerals. It represents mourning.
Like I said, this is a very general overview. If there's anything I can do to help, as here, or message me.
If I made any mistakes or something isn't clear, let me know.