Red is the color of Pentecost

"The main sign of Pentecost in the West is the color red. It symbolizes joy and the fire of the Holy Spirit. 

Priests or ministers, and choirs wear red vestments, and in modern times, the custom has extended to the lay people of the congregation wearing red clothing in celebration as well. Red banners are often hung from walls or ceilings to symbolize the blowing of the "mighty wind" and the free movement of the Spirit. 

The celebrations may depict symbols of the Holy Spirit, such as the dove or flames, symbols of the church such as Noah's Ark and the Pomegranate, or especially within Protestant churches of Reformed and Evangelical traditions, words rather than images naming for example, the gifts and Fruits of the Spirit. Red flowers at the altar/preaching area, and red flowering plants such as geraniums around the church are also typical decorations for Pentecost masses/services. These symbolize the renewal of life, the coming of the warmth of summer, and the growth of the church at and from the first Pentecost. In the southern hemisphere, for example, in southern Australia, Pentecost comes in the mellow autumntide, after the often great heat of summer, and the red leaves of the poinsettia have often been used to decorate churches then. 

In some cases, red fans, or red handkerchiefs, are distributed to the congregation to be waved during the procession, etc. Other congregations have incorporated the use of red balloons, signifying the "Birthday of the Church". These may be borne by the congregants, decorate the sanctuary, or released all at once."