So far, the synth background is black. I have it embed in my website, but the black background doesn't match my white website.

Is there anyway to indicate the background color of it? Thanks a lot.

No, there unfortunately isn't an option to change the background color.

Thanks a lot. Is there anyway to recommand new features to Photosynth service? I really love it. Thanks a lot.

I recommend either the Suggestions forum here on Photosynth.net, their Get Satisfaction community which preceded the Photosynth.net forums, or emailing the team directly. 

Here is the link to the Suggestions Forum: 
http://photosynth.net/forum.aspx?cat=01b6f15f-42eb-49cb-a221-ed56615e1c47

Here is the link to the Get Satisfaction community: 
http://getsatisfaction.com/livelabs

Here is the Contact Us page for Photosynth: 
http://photosynth.net/contactus.aspx

Here is the link for a somewhat related discussion: 
http://photosynth.net/discussion.aspx?cat=01b6f15f-42eb-49cb-a221-ed56615e1c47&dis=3fc3fb64-876e-48a0-a113-1b0b07c6d0d8