I know how to lighten the colors for certain commands, however I'd like to lighten the standard ansi colors across all commands.
I found instructions for doing it for Xterm and aterm here:
http://gentoo-wiki.com/TIP_Linux_Colors_in_Aterm/rxvt
From those I was able to get brighter colors by adding:
rxvt*background: #000000
rxvt*foreground: #7f7f7f
rxvt*color0: #000000
rxvt*color1: #9e1828
rxvt*color2: #aece92
rxvt*color3: #968a38
rxvt*color4: #414171
rxvt*color5: #963c59
rxvt*color6: #418179
rxvt*color7: #bebebe
rxvt*color8: #666666
rxvt*color9: #cf6171
rxvt*color10: #c5f779
rxvt*color11: #fff796
rxvt*color12: #4186be
rxvt*color13: #cf9ebe
rxvt*color14: #71bebe
rxvt*color15: #ffffff
to the bottom of my ~/.Xdefaults file