]Thanks for the quick reply !
It works fine with all browsers.
The only case where I have a black backgound is when I render a chart with UIWebView in my iphone app (I use PhoneGap).
When I access the mobile version of my site with an iPhone & Safari, the chart background is ok (white).
When I access it through my iPhone app, the background & canvas background are black.
Screenshots are attached.
Alex