setting cellBackColor after init doesn't work

Rob,

Are you using cssOnly = true?

In the CssOnly mode cellBackColor is ignored and you should use the css theme or onBeforeCellRender to change the cell color.

I use cssOnly = false

This issue is fixed now in build 7.7.698 (see the sandbox):

http://javascript.daypilot.org/sandbox/

I executed the script below in the debug console of my browsers (FF 27 beta, Chrome 32 and IE9) when visiting the sandbox and it doesn't seem to work.

dp.cssOnly = false;
dp.update(); // Css drops and raw styling on elements appears
dp.cellBackColor = "#FF0000";
dp.update(); // Only cells that are 'new' will get the red color (so when no scrolling was done before the cells after June 2013 in the sample

The already-rendered values were cached. Build 7.7.700 should fix that as well.