In PowerBI embedded reports, the default data colors for a chart with a differentiating legend merge into one, thereby removing the legend visualization capability.
Example/Bug: Bar chart with axis, legend, and values. Legend colors (default) green and gray, upon loading the embedded report the first default color (green in this case) is used to represent the values for what was originally both green and gray.
By setting custom colors instead of keeping the default, the individuality of each legend variable is kept and the chart accurately shows each color.