Four coloured lamps are arranged in a 2×2 array, where the letters R, Y, B and W represent the colours red, yellow, blue and white respectively. Each  lamp changes its colour every minute. In the first minute, the colours of the lamps in the two rows are interchanged.  In the second minute, colours of the lamps in the two columns are interchanged. See the diagram below. This cycle is then repeated. What are the colours of the four lamps at the 60^th minute?