A problem with color is that people end up optimizing the aesthetics for their own terminal setup. There is a wild number of different color schemes out there and it's really hard to make something that looks good on all of them. In my experience the only safe choice is bold text (i.e. \033[1m) since it stands out in all cases.
red, yellow, green, cyan, and magenta are pretty safe. We've had complaints about others, but these are pretty reliable in my experience. dim is safe too, but doesn't work all the time. (Not working meaning just not dimmed)
I would definitely not call yellow a safe color. I use a terminal with a white background, and yellow text is unreadable unless the text is also given a custom background color.
