Disable colours at runtime in xterm

I would like to disable colours in my xterm at runtime. Reason being that some programs lack the sanity to use them in proper way.

For example:

$ sane-program
color output

$ disable-color
$ less-sane-program
black-white output

$ enable-color
$ sane-program
color output

I know I can use xterm -cm, or change colorMode in my ~/.Xdefaults, but that requires starting new xterm. I tried setting TERM to xterm-old or an invalid string (arggggh), but I still have colours. xtermcontrol also doesn't have an option.

Ctrl+right click and deselecting "Allow color ops" doesn't seem to do anything either (it would be cool if this worked).

Filtering out the colour codes with sed is the workaround I use now, but this doesn't work for interactive programs...