VasmCC will behave according to what WM you're running.
If you run KDE, you contol it's fonts and colors from qtconfig
if you run GNOM, XFCE, LXDE, or any other GTK+ oriented WM, you control it with GTK
try using gtk-chtheme or your WM's config utility
Thanks. I worked that one out (

by reducing the VasmCC fonts to the point that they could hardly be seen..)
The fonts in the external dialogs (the ones that pop up after you click on vasmCC) are controlled by the gtk configuration all the time IIRC

I had a look at the gtk config stuff, but couldn't make much sense of it. For the moment, upgrading xdialog seems to have fixed the problem, though I still can't work out why the font size changed in the first place.
Still, looks much better now....
paul.