Yeah, I don't think the color change with that Stapelia is an indication of unhappiness, necessarily. Stress colors (the purplish brown with that plant for example) are often a response to sun, perfectly normal, perfectly reversible (up to a point of course), and not necessarily a sign that anything about care needs to change.
To each their own, of course, these observations made after years of moving these plants around on the patio and noting how they change in appearance depending on exposure. I have tried to figure out which stress colors are an indicator of something wrong and which stress colors are just an effect of the season or whatever, and can be enjoyed without concern for the plant's well being. To be honest I generally favor plants with the stress colors on, compared to the green versions, if given a choice.
