Any umbrella with a long enough shaft to clear your head when stick in your sternum strap at the shoulder harness junction will provide welcome shade. I have used formal trekking umbrellas and am of the considered opinion that a conventional umbrella, in light color, provides a cost-effective portable shade screen. It is also suitable to use in light rainfall.
To mitigate the weight penalty of using the umbrella, consider using a long sleeve synthetic polo shirt in place of a fleece garment. Also, if you are using a poncho for heavy rain, a separate rain parka is redundant. Obviously, this works better for a Jun - August Camino than it would for a spring or fall Camino, when colder weather is likely.
I recommend trying something you already own. Black, dark green, navy blue, or a wine color attracts the heat from the sun. White, yellow, light green or blue do a better job at providing shade while reflecting much of the sun's heat...just sayin...
Hope this helps.