as i said... i could do that later... but it's the same as in the SMS-css... so you only have to open the sms-css and the im-css next to each other and look at the names and values .... and change them. ^^

btw: bringing color in the sms-conversation
(you can use the whole color-range of the n900... colors can be changed by editing the value behind "background:" in the bubbles-block (in css-file))
short color-table here: http://www.w3schools.com/CSS/css_colors.asp
bubble-borders to use: http://de.selfhtml.org/css/eigenscha...rder_style.htm
(as you see bubble-color can be defined as well - for every edge: http://de.selfhtml.org/css/eigenscha...rder_color.htm)
you can change the font to every installed font-type (don't know which types these are) http://de.selfhtml.org/css/eigenscha...ont_family.htm - it's possible to edit color and add shadow too: http://de.selfhtml.org/css/eigenscha...ext_shadow.htm

edit: second screenshot with borderstyles groove and ridge (too bad the second border color is always so dark - maybe can't tell dark-color and black apart)