function windIntensityColorScale(step, maxWind) {
        var result = [];
        for (var j = 85; j <= 255; j += step) {
            result.push(asColorStyle(j, j, j, 1.0));
        }
        result.indexFor = function(m) {  // map wind speed to a style
            return Math.floor(Math.min(m, maxWind) / maxWind * (result.length - 1));
        };
        return result;
    }
@returns {Array} of wind colors and a method, indexFor, that maps wind magnitude to an index on the color scale.