If your palette does not have good contrast between foreground colors 31-37 and background color 40, that's on you. If you cange the default background color to something other than 40 that's also on you - if you want the default background to be white, change the palette so that color 40 is white (instead of changing the backgound color to e.g. 47) and make the foreground colors dark enough so that they contrast well.