def colour_column_volc(df, xcol, ycol):
    """Generates red/blue/gray colour column for volcano plot data according to the value in x and y cols for each protein."""
    df['colours'] = 'gray'
    df.loc[(df[xcol] > 1) & (df[ycol] > 1.3), ['colours']] = 'red'
    df.loc[(df[xcol] < -1) & (df[ycol] > 1.3), ['colours']] = 'blue'
    return df