Studying the description of their powers and the tiny blurb we get about the class I got wondering about the style and themeing of the class.
Solarians by contrast seem to be about balance of extremes. Stylistically they use a mixture of bright solar tones and darker gravity ones. But always there is a balance. They have a graceful monastic design with robes, loose clothing, and glowing manifestations of their power in iconic shapes. Sword/armor, etc. The Jedi of Star Wars, the Clerics of Equalibrium, the hackers of The Matrix.
But when I think of Vanguards...something else comes to mind. They are armored, carry shields. Run down attacks almost gleefully inviting destruction and harm to begin the generation of their strikes. It screams PUNK, brighter neon colors, mismatch designs. Haphazard yet functional. They are very much the drunk masters of the Starfinder setting. I'd see them in stark cut armor with overly bright logos and symbols of disaster and harm. Nuclear Warning logos, Mangled hand warnings on riot shields, road signs showing falling rocks.
Their embrace of entropy and the role it plays in the universe screams they go out and "live life to the fullest". A strong joyful nihilism, death may come but what of it? It is the nature of things, go, live, experience. Yes they train in monasteries, but that's just to learn to self control needed to harness their power. But no Vanguard's training is complete until they step out into the universe, bash their heads against it, and come back years later weathered and scared from the joy of the experience.
Vanguard masters would be living tapestries of life lived to the fullest. Covered with scars, tattoos, as living textbooks on how to face down entropy itself and harness it for self discovery.
tl:dr: Think Tank Girl meets 80's action figures. Gritty and Bright!