The DRAW_COLOR_LINE drawing style is used to plot lines with different colors, the colors are specified in the color buffer.
Two indicator buffers are used: the first contains the closing price of the bar, the color indexes specified in the second indicator buffer. The colors of lines, the width and line style changed randomly after N=5 ticks. The initial properties of the plot1 graphic plot are defined using the #property preprocessor directive, further these properties changed randomly (see OnCalculate() function).
See also The Drawing Styles in MQL5.