Carl is mentioned to have been a leading figurehead for neosymbolism in the 2020s. Neosymbolism is an art movement that focuses primarily on (you guessed it) symbols as a way of communicating modern concepts and truths. It leans into mysticism, spirituality, and dreams strongly, and holds its art as a contrast to commercialized art.
Carl uses blue in a shitton of his paintings. Historically blue as a color has a plethora of meanings. This could be a reference to any of those, but seeing how it’s frequently used as a liquid over a human form here, as well as for flesh and body colors, it’s also probably a reference to androids and Blue Blood.
As a symbol, Blue Blood may be as visually understandable in 2038 as toxic rainbow patterns on an oil slick are now. On a practical level, Blue Blood is a critical part of what keeps androids fueled and functioning properly, and androids themselves are a symbol that mean everything from ‘hope and an easier, better future’ to ‘machines taking over everything and leaving humans screwed’. Considering Carl, he may be using art as a way to discuss the relationship between androids and humans, and androids and their personhood.
(It’s probably possible to read in to the fact that most of his paintings don’t have their eyes open and aren’t looking at the viewer, but on a less in-universe note, his paintings are incredibly simple, and the paintings’ real-world artists may have been focusing more on ‘let’s make some artifacts for a video game so we can tell he paints a lot’, rather on ‘what are the hidden truths Carl Manfred dreams about at night’.)
Philosophy-wise, what we see from Carl in the game is a lot of focusing on what makes a person human. He talks about humans being fragile machines, discusses Markus’ growing independence and creativity, and talks about the need to stand up for one’s self in a hostile world. He seems to be encouraging the parts of Markus that are spiritual, and that rely on critical and abstract thought, and individuality.
He complains about the attendees of the cocktail party he and Markus are returning from at the beginning of Chapter 8 (Broken). His specific complaints are that they’re commercially focused, and that they’re boring.
